I suggest   use this plugin   to add snippets   (otherwise you should create child theme  and put code to  functions.php )

These snippets are ordered by complexity levels

Beginner

// add order prefix
add_filter('woe_get_order_value_order_number','woe_format_order_number', 10, 4);
function woe_format_order_number($value, $order, $item, $product) {
	return "KTR-" . $value;
}
// custom Shipping Full Name  ( last + first )
add_filter('woe_get_order_value_shipping_full_name',function ($value, $order,$fieldname) {
	return get_post_meta($order->id,'_shipping_last_name',true) . ' '  . get_post_meta($order->id,'_shipping_first_name',true);
},10,3);
// Update order status after export 
add_action('woe_order_exported', function ($order_id) {
    $order = new WC_Order($order_id);
    $order->update_status('completed', '');
} ); 
// sort products by SKU, inside order
add_filter('woe_fetch_order_products','woe_sort_products_by_sku', 10, 5);
function woe_sort_products_by_sku($products, $order, $labels, $format, $static_vals) {
	usort($products, function($a, $b){
		if ($a['sku'] == $b['sku']) return 0;
		return ($a['sku'] < $b['sku']) ? -1 : 1;
	});
	return $products;
}
// add product field "Quantity x Name"
add_filter('woe_get_order_product_fields', 'add_product_two_fields', 10, 2);
function add_product_two_fields($fields,$format) {
	$fields['qty_name'] = array( 'label' => 'Quantity x Name', 'colname' => 'Quantity x Name', 'checked' => 1 );
	return $fields;
}
add_filter('woe_get_order_product_value_qty_name', 'get_product_addon_qty_name', 10, 4);
function get_product_addon_qty_name($value,$order, $item, $product) {
	return $item['qty'] .' x '. $item['name'];
}
// format product weight, 0.2->0.200  and 0.12->0.120
add_filter('woe_get_order_product_value_weight','woe_format_weight', 10, 4);
function woe_format_weight($value, $order, $item, $product) {
	return number_format($value,3,'.','');
}
//remap shipping method titles
add_filter('woe_get_order_value_shipping_method_title','woe_rename_shipping_method_title', 10, 4);
function woe_rename_shipping_method_title($value, $order, $item, $product) {
 if($value == 'UK Standard Shipping') // copy these 2 lines for other mappings
        return 'STANDARD';            // copy these 2 lines for other mappings
 return $value;
}
// don't export orders with total < 1
add_filter( 'woe_fetch_order_row', 'woe_filter_orders_by_sum',10,2);
function woe_filter_orders_by_sum( $row,$order_id ) { 
  return ($row['order_total']<1) ? false : $row;
}
// add new date format 20161231, see more http://php.net/date
// You have to select new format in dropdown "Date" ( section "Format")
add_filter('woe_date_format', 'woe_add_date_format');
function woe_add_date_format($s) {
 $s[] ='Ymd';
 return $s;
}
// CSV without quotes
add_filter('woe_csv_custom_output_func','woe_csv_no_quotes', 10, 6);
function woe_csv_no_quotes($custom_output,$handle,$data,$delimiter,$linebreak,$enclosure) {
	fwrite($handle, join($delimiter, $data)."\r\n" );
	$custom_output = true; //stop fputcsv!
	return $custom_output;
}
// CSV force quotes
add_filter('woe_csv_custom_output_func',function ($custom_output,$handle,$data,$delimiter,$linebreak,$enclosure) {
	foreach($data as $k=>$v) 
		$data[$k] =  $enclosure . str_replace($enclosure, $enclosure . $enclosure, $v) . $enclosure;
	fwrite($handle, join($delimiter, $data). $linebreak  );
	return true;  //stop default fputcsv!
}, 10, 6);
// modify Content-Type for HTTP Post ( Pro version)
add_filter('wc_order_export_http_args', function ($args) {
	$args['headers']['Content-Type'] = "text/csv";
	return $args;
});

Competent

// add new field "shipping + tax"
add_filter('woe_get_order_fields', 'woe_addd_shipping_plus_tax_field' );
function woe_addd_shipping_plus_tax_field($fields) {
	$fields['order_shipping_plus_tax'] = array('segment'=>'cart','label'=>'Order shipping plus tax','colname'=>'Order shipping plus tax','value'=>'','checked'=>1);
	return $fields;
}
add_filter('woe_get_order_value_order_shipping_plus_tax','woe_fill_order_shipping_plus_tax', 10, 4);
function woe_fill_order_shipping_plus_tax($value, $order, $item, $product) {
	return $order->order_shipping+$order->order_shipping_tax;
}
 // new column "All Fees"
add_filter('woe_get_order_fields', function ($fields) {
	$fields['all_fees'] = array( 'label' => 'All Fees', 'colname' => 'All Fees', 'checked' => 1 );
	return $fields;
});
add_filter('woe_get_order_value_all_fees', function ($value,$order) {
	$result = 0; 	
	foreach($order->get_items('fee') as $fee) {
		$result += $fee['line_total'];
	}
	return $result;
},10, 2);
//convert "order total" and "item price"  from CNY to USD
class WOE_currency_mod {
	var $rate = false;
	
	function __construct() {
		add_filter('woe_get_order_value_order_total',array($this,'convert_cny_usd'), 10, 2);
		add_filter('woe_get_order_product_value_item_price',array($this,'convert_cny_usd'), 10, 2);
	}	
	
	function convert_cny_usd($value, $order) {
		return round( $value * $this->get_rate(), 2 );
	}
	
	function get_rate() {
		if( $this->rate === false) {
			$response = wp_remote_get("http://api.fixer.io/latest?base=CNY&symbols=USD");
			$api_response = json_decode( wp_remote_retrieve_body( $response ), true );
			$this->rate = $api_response['rates']['USD'];
		}
		return $this->rate;
	}
}	
new WOE_currency_mod();
// sort by usernames using SQL filters
add_filter('woe_sql_get_order_ids_left_joins','woe_join_usernames');
function woe_join_usernames($joins) {
	global $wpdb;
	$joins[] = "LEFT JOIN {$wpdb->postmeta} AS order_usernames ON (order_usernames.post_id = orders.ID AND order_usernames.meta_key='_customer_user')";
	$joins[] = "LEFT JOIN {$wpdb->users} AS users ON users.ID = order_usernames.meta_value";
	//var_dump($joins);	die();
	return $joins;
}
add_filter('woe_sql_get_order_ids_fields','woe_set_select_fields');
function woe_set_select_fields($fields) {
 	return "orders.ID AS order_id,users.user_login AS username";
 }
add_filter('woe_sql_get_order_ids_order_by','woe_sort_orders_by_usernames');
function woe_sort_orders_by_usernames($order_by) {
	return "ORDER BY username";
}
//export Shipping line as Product 
add_filter('woe_fetch_order_products','woe_add_shipping_as_products', 10, 5);
function woe_add_shipping_as_products($products,$order,$labels, $format, $static_vals) {
	$i = count ($products);
	foreach ( $order->get_items('shipping') as $item_id=>$item ) {
		$row = array();
		$i++;
		$item["taxes"] = unserialize($item["taxes"]);
		foreach ( $labels as $field => $label ) {
			if ( $field == 'line_id' ) {
				$row[ $field ] = $i;
			} elseif ( $field == 'sku' ) {
				$row[ $field ] = $item["method_id"];
			} elseif ( $field == 'name' ) {
				$row['name'] = $item["name"];
			} elseif ( $field == 'qty' ) {
				$row['qty'] = 1;
			} elseif ( $field == 'item_price' ) {
				$row['item_price'] = $item["cost"] + array_sum($item["taxes"]);
			} elseif ( $field == 'price' ) {
				$row['price'] = $item["cost"]  + array_sum($item["taxes"]);
			} elseif ( isset( $static_vals[ $field ] ) ) {
				$row[ $field ] = $static_vals[ $field ];
			} 
		}
		$products[] = $row;
	}
	return $products;
}
// add field "Date Processed", based on order's comments
add_filter('woe_get_order_fields', 'woe_func_add_order_fields');
function woe_func_add_order_fields($fields) {
    $fields['date_processed'] = array( 'label' => 'Date Processed', 'colname' =>'Date Processed', 'segment' => 'user', 'checked' => 1 );
    return $fields;
}
add_filter('woe_get_order_value_date_processed','woe_get_value_date_processed',10, 2);
function woe_get_value_date_processed($value,$order) {
    $args = array(
		'post_id' 	=> $order->id,
		'approve' 	=> 'approve',
		'type' 		=> 'order_note',
		'search'        => 'Order status changed from Pending Payment to Processing.',
    );
    // woocommerce hides such records by default
    remove_filter( 'comments_clauses', array( 'WC_Comments', 'exclude_order_comments' ), 10 );
    $notes = get_comments( $args );
    add_filter( 'comments_clauses', array( 'WC_Comments', 'exclude_order_comments' ), 10, 1 );

    $date_processed = '';
    if(!empty($notes)) {
        $date_processed = date("m/d/Y",strtotime($notes[0]->comment_date)); // to US format
    }
    return $date_processed;
}
//customize json 
class WOE_add_customer_json {
	function __construct() {
		add_filter('woe_fetch_order_row',array($this,'woe_remember_order_id'), 10, 2);
		add_filter('woe_json_output_filter', array($this,'woe_add_json_customer'), 10, 2);
	}	

	function woe_remember_order_id($row,$order_id) {
		$this->order_id = $order_id;
		return $row;
	}

	function woe_add_json_customer($json,$data) {
		$order = new WC_Order($this->order_id);
		//add new customer
		$data['customer'] = array();
		$data['customer']['name'] = $order->shipping_first_name." ".$order->shipping_last_name;
		$data['customer']['email'] = $order->billing_email;
		$data['customer']['phone'] = $order->billing_phone;
		$data['customer']['address1'] = $order->shipping_address_1;
		$data['customer']['address2'] = $order->shipping_address_2;
		$data['customer']['city'] = $order->shipping_city;
		$data['customer']['state'] = $order->shipping_state;
		$data['customer']['country'] = $order->shipping_country;
		$data['customer']['zip'] = $order->shipping_postcode;
		return json_encode($data,JSON_PRETTY_PRINT);
	}
}	
new WOE_add_customer_json();

Expert

 // custom XML
add_filter("woe_xml_output_filter","woe_xml_make_order");
function woe_xml_make_order($xml) {
 // get order 
 $order = new WC_Order(WC_Order_Export_Data_Extractor::$current_order);

 //make xml
 $xml = new SimpleXMLElement( "<Order/>" );

 // top
 $xml->addChild("OrderNumber", $order->get_order_number() );
 $xml->addChild("CustomerNumber", $order->user_id );

 // addresses
 $addr = $xml->addChild("Addresses");
 $b_addr = $addr->addChild("BillingAddress");
 $b_addr->addChild("FirstName",$order->billing_first_name);
 $b_addr->addChild("LastName",$order->billing_last_name);
 $b_addr->addChild("Street", trim( $order->billing_address_1. " " . $order->billing_address_2) );
 $b_addr->addChild("Zipcode",$order->billing_postcode);
 $b_addr->addChild("City",$order->billing_city);
 $s_addr = $addr->addChild("ShippingAddress");
 $s_addr->addChild("FirstName",$order->shipping_first_name);
 $s_addr->addChild("LastName",$order->shipping_last_name);
 $s_addr->addChild("Street", trim( $order->shipping_address_1. " " . $order->shipping_address_2) );
 $s_addr->addChild("Zipcode",$order->shipping_postcode);
 $s_addr->addChild("City",$order->shipping_city);

 // items
 $items = $xml->addChild("LineItems");
 foreach ( $order->get_items('line_item') as $item_id=>$item ) {
   $product   = $order->get_product_from_item( $item );
   $item_meta = $order->get_item_meta( $item_id );

   $itemXML = $items->addChild("LineItem");
   $itemXML->addChild("Id",$product->sku);
   $itemXML->addChild("Name",$item['name']);
   $itemXML->addChild("Quantity",$item['qty']);
 }
 

 // shipment 
 $ship = $xml->addChild("LineItemShipping");
 $shipping_methods = $order->get_items( 'shipping' );
 $shipping_method = reset($shipping_methods); // take first entry
 $shipping_method_id =  !empty($shipping_method) ?  $shipping_method['method_id'] : '' ;
 $ship->addChild("Id",$shipping_method_id);
 $ship->addChild("TotalPrice",$order->get_total_shipping() );
 $ship->addChild("Name",$order->get_shipping_method() );

 // payment 
 $pay = $xml->addChild("LineItemPayment");
 $pay->addChild("Id",$order->payment_method);
 $pay->addChild("TotalPrice",$order->get_total() );
 $pay->addChild("Name",$order->payment_method_title );

 //bottom
 $xml->addChild("CreationDate", $order->order_date );
 $xml->addChild("ShippedOn", $order->completed_date );

 //format it!
 $dom = dom_import_simplexml( $xml );
 $dom->ownerDocument->formatOutput = true;
 return  $dom->ownerDocument->saveXML( $dom->ownerDocument->documentElement );
}
//add all taxes as columns
class WOE_add_all_taxes{
	var $taxes;
	
	function __construct() {
		add_filter('woe_get_order_fields', array($this,'add_order_fields'), 10, 1);
		add_filter('woe_order_export_started',array($this,'fetch_order_taxes'), 10, 1);
	}	
	
	function add_order_fields($fields) {
		global $wpdb;
		
		$taxes = $wpdb->get_results("SELECT * FROM {$wpdb->prefix}woocommerce_tax_rates");
		foreach($taxes  as $tax) {
			$fields['tax_'.$tax->tax_rate_id] = array('label'=>$tax->tax_rate_name,'checked' => 1, 'segment'=>'cart','colname'=>$tax->tax_rate_name);
			add_filter('woe_get_order_value_tax_'.$tax->tax_rate_id, array($this,'get_tax_value'), 10, 3);
		}	
		return $fields;
	}
	

	function fetch_order_taxes($order_id) {
		//reset values
		$this->taxes = array();
		//read taxes
		$order = new WC_Order($order_id);
		foreach($order->get_tax_totals() as $code=>$tax) {
			$this->taxes['tax_'.$tax->rate_id ] =  wc_round_tax_total($tax->amount);
		}
                return $order_id;
	}
	
	function get_tax_value($value, $order,$field) { 
		return isset($this->taxes[$field]) ? $this->taxes[$field] : 0;
	}
}	
new WOE_add_all_taxes();
// Summary by Products , see conditions below! 
// Format - CSV
// Button - Export w/o Progressbar 
class Woe_Summary_Products {
	function __construct() {
		$this->summary_products = array();
		$this->products_data = array();
		
		add_action("woe_settings_above_buttons", array($this,"draw_summary_products") );
		add_action("woe_order_export_started", array($this,'record_order_products') );
		add_filter("woe_csv_custom_output_func", array($this,'skip_order_line')  );
		add_action("woe_csv_print_footer", array($this,'print_summary_products') );
	}

	function draw_summary_products($settings){
		$selected = !empty($settings[ 'summary_by_products' ]) ? 'checked': '';
		$selected_2 = !empty($settings[ 'skip_orders' ]) ? 'checked': '';
		echo '<br><br>
		<input type=hidden name="settings[summary_by_products]" value="0">
		<input type=checkbox name="settings[summary_by_products]" value="1" '. $selected .'>
		<span class="wc-oe-header">Summary Report by products for CSV (Export w/o progressbar)</span>
		<input type=hidden name="settings[skip_orders]" value="0">
		<input type=checkbox name="settings[skip_orders]" value="1" '. $selected_2 .'>
		Don\'t output orders 
		<br><br>';
	}

	function record_order_products($order_id) {
		if( empty(WC_Order_Export_Engine::$current_job_settings['summary_by_products']) )
			return $order_id;
		
		$order  = new WC_Order($order_id);
		foreach($order->get_items( ) as $item) {
			$name = $item['name'];
			if(!isset($this->summary_products[$name]))
				$this->summary_products[$name] = 0;
			$this->summary_products[$name] += $item['qty'];
			
			//gather common product details 
			if( !isset($this->products_data[$name])) {
				$product   = $order->get_product_from_item( $item );
				$this->products_data[$name]['sku'] = $product ? $product->get_sku() : '';
			}	
		}
                return $order_id;
	}
	
	function skip_order_line($custom_export) {
		if( !empty(WC_Order_Export_Engine::$current_job_settings['skip_orders']) )
			return true;
		return $custom_export;	
	}
	
	function print_summary_products($f) {
		if( empty(WC_Order_Export_Engine::$current_job_settings['summary_by_products']) )
			return ;
		
		//empty line to split orders and summary
		if( empty(WC_Order_Export_Engine::$current_job_settings['skip_orders']) ) {
			fputcsv( $f,  array(), WOE_Formatter_Csv::$delimiter, WOE_Formatter_Csv::$enclosure  );
		}	
			
		ksort($this->summary_products);// by name 
		
		$data = array("SKU","Product", "Quantity");
		fputcsv( $f, $data, WOE_Formatter_Csv::$delimiter, WOE_Formatter_Csv::$enclosure );
			
		foreach($this->summary_products as $name=>$qty) {
			$sku = $this->products_data[$name]['sku'];
			$data = array($sku,$name,$qty);
			fputcsv( $f, $data, WOE_Formatter_Csv::$delimiter, WOE_Formatter_Csv::$enclosure );
		}
	}
}
new Woe_Summary_Products ();
// Pro version, send separate CSV to each seller
class Woe_Seller_CSV_mod {
	function __construct() {
		add_action("woe_test_destination", array($this,"add_hooks") );
		add_action("woe_start_cron_job_1", array($this,"add_hooks") ); // adjust job ID here 
	}
	
	function add_hooks () {
		add_action("woe_formatter_csv_start", array($this,"csv_start"),10,1);
		add_action("woe_order_export_started",array($this,"start_new_order"),10,1);
		add_action("woe_get_order_product",array($this,"detect_seller"),10,1);
		add_action("woe_formatter_set_handler_for_csv_row",array($this,"switch_file"),10,1);
		add_action("woe_formatter_csv_finished",array($this,"close_csv_files"),10,1);
		add_action("woe_custom_export_to_email",array($this,"send_csv_files"),10,4);
	}

	function csv_start($header) {
		$this->header = $header;
		$this->filenames = $this->files = array();
	}

	function start_new_order($order_id) {
		//remember sellers is for rows here 
		$this->product_sellers = array();
		$this->product_sellers_pos = 0;
                return $order_id;
	}

	function detect_seller($product) {
		$seller_id = $product->post->post_author;
		
		// remember seller  sequence for rows
		$this->product_sellers[] = $seller_id; 
		
		//put header to new file
		if( !isset($this->files[$seller_id]) ) {
			$this->filenames[$seller_id] = tempnam("/tmp",$seller_id);
			$this->files[$seller_id] = fopen( $this->filenames[$seller_id], "wb+");
			fputcsv($this->files[$seller_id], $this->header);
		}
	}

	function switch_file($handle) {
		$seller_id = $this->product_sellers[$this->product_sellers_pos++];
		return $this->files[$seller_id];
	}
	
	function close_csv_files() {
		foreach($this->files as $f)
			if(get_resource_type($f) == 'stream')
				fclose($f);
	}
	
	function send_csv_files($processed, $filename, $filepath, $exporter) {
		global $ts_mail_errors;
		
		foreach($this->filenames as $seller_id => $filepath) { // override filepath
			$user_info = get_userdata($seller_id);
			if( !empty($user_info->user_email) ) {
				$exporter->destination['email_recipients'] = $user_info->user_email;//override email
				$ts_mail_errors = array();
				echo $exporter->run_export( $filename, $filepath )."\n";
			}	
		}
		return true;
	}
}
new Woe_Seller_CSV_mod();