Pokud je potřeba vložit nějaký obsah do Woocommerce emailů:

Woocommerce email hooks

woocommerce_email_header ($email_heading, $email)
woocommerce_email_order_details ($order, $sent_to_admin, $plain_text, $email)
woocommerce_email_before_order_table ($order, $sent_to_admin, $plain_text, $email)
woocommerce_order_item_meta_start($item_id, $item, $order, $plain_text)
woocommerce_order_item_meta_end ($item_id, $item, $order, $plain_text)
woocommerce_email_after_order_table ($order, $sent_to_admin, $plain_text, $email)
woocommerce_email_order_meta ($order, $sent_to_admin, $plain_text, $email)
woocommerce_email_customer_details ($order, $sent_to_admin, $plain_text, $email)
woocommerce_email_footer($email)

Příklad 1

<?php
add_action( 'woocommerce_email_header', 'mm_email_header', 10, 2 );
function mm_email_header( $email_heading, $email ) { 
	echo "<p> Thanks for shopping with us. We appreciate you and your business!</p>";
}

Příklad 2

<?php
add_action( 'woocommerce_email_after_order_table', 'mm_email_after_order_table', 10, 4 );
function mm_email_after_order_table( $order, $sent_to_admin, $plain_text, $email ) { 
       echo "<p>Hey! Thanks for shopping with us. As a way of saying thanks, here’s a coupon code for your next purchase: FRESH15</p>";
}

Příklad 3

<?php
add_action( 'woocommerce_email_footer', 'mm_email_footer', 10, 1 );
function mm_email_footer( $email ) { ?>
	<p><?php printf( __( 'Thank you for shopping! Shop for more items using this link: %s', 'woocommerce' ), '<a href="' . get_permalink( wc_get_page_id( 'shop' ) ) . '">' . __( 'Shop', 'woocommerce' ) . '</a>' ); ?></p>

<?php
}

Může se hodit…

Pokud je potřeba vložit obsah jen do některých e-mailů, je třeba dát podmínku

if( 'customer_processing_order' == $email->id ){
...
}

kde

$email-id

může být:

new_order
customer_on_hold_order
customer_processing_order
customer_completed_order
customer_refunded_order
customer_partially_refunded_order
cancelled_order
failed_order
customer_reset_password
customer_invoice
customer_new_account
customer_note

Reference

https://stackoverflow.com/questions/47741577/targeting-specific-email-with-the-email-id-in-woocommerce

https://stackoverflow.com/questions/41474248/customizing-customer-processing-emails-notification-in-woocommerce