Add info to WooCommerce order emails -

custom-note-to-order-email.php

<?php
/*
Plugin Name: Custom note to order email
Plugin URI: https://www.damiencarbery.com/2018/07/add-info-to-woocommerce-order-emails/
Description: Add a note to the order email if the order contains products from the specified category.
Author: Damien Carbery
Version: 0.1
*/

/* Add note about shapetrousers delivery time to the order email. */
add_action( 'woocommerce_email_order_details', 'am_shapetrousers_delivery_info_to_order_email', 5, 4 ); 
function am_shapetrousers_delivery_info_to_order_email( $order, $sent_to_admin, $plain_text, $email ) {
	// Only customers need to know about the delivery times.
	if ( $sent_to_admin ) {
		return;
	}

	$order_has_shapetrousers_product = false;

	$items = $order->get_items();
	foreach ( $items as $item_id => $item ) {
		$product = $item->get_product();
		if ( $product->is_type( 'variation' ) ) {
			$product = wc_get_product( $product->get_parent_id() );
		}

		if ( has_term( 'shapetrousers', 'product_cat', $product->get_id() ) ) {
			$order_has_shapetrousers_product = true;
		}
	}
	
	if ( $order_has_shapetrousers_product ) {
		if ( $plain_text ) {
			echo "\nNOTE: Shapetrousers products are custom made so please allow 10 days for delivery.\n";
		}
		else {
			echo '<p><strong>Note</strong>: Shapetrousers products are custom made so please allow 10 days for delivery.</p>';
		}
	}
}

email-template-layout.php

<?php
do_action( 'woocommerce_email_header', $email_heading, $email );
do_action( 'woocommerce_email_order_details', $order, $sent_to_admin, $plain_text, $email );
do_action( 'woocommerce_email_order_meta', $order, $sent_to_admin, $plain_text, $email );
do_action( 'woocommerce_email_customer_details', $order, $sent_to_admin, $plain_text, $email );

processing-email-only.php

<?php
/*
Plugin Name: Note for Processing email
Plugin URI: https://www.damiencarbery.com/2018/07/add-info-to-woocommerce-order-emails/
Description: Add a note to the processing order email only.
Author: Damien Carbery
Version: 0.1
*/

add_action( 'woocommerce_email_order_details', 'am_note_for_processing_order_email', 5, 4 ); 
function am_note_for_processing_order_email( $order, $sent_to_admin, $plain_text, $email ) {
	// Only customers need to know about the delivery times.
	if ( $sent_to_admin ) {
		return;
	}

	if ( 'customer_processing_order' == $email->id ) {
		if ( $plain_text ) {
			echo "\n** We are working on your order right now. It is our top priority - we will skip meals to get it ready for you!\n";
		}
		else {
			echo '<p>We are working on your order <strong>right now</strong>. It is our <strong>top priority</strong> - we will skip meals to get it ready for you!</p>';
		}
	}
}

tracking-info-to-woo-email.php

<?php
/*
Plugin Name: Add tracking info to Completed Order email
Plugin URI: https://www.damiencarbery.com/2018/07/add-info-to-woocommerce-order-emails/
Description: Add tracking info to the Complete Order email (replying to Joel's comment).
Author: Damien Carbery
Version: 0.1
*/


add_action( 'woocommerce_email_customer_details', 'dcwd_add_tracking_info_to_completed_order_email', 30, 4 );
function dcwd_add_tracking_info_to_completed_order_email( $order, $sent_to_admin, $plain_text, $email ) {
	if ( 'customer_completed_order' != $email->id ) {
		return;
	}
	if ( $sent_to_admin ) {
		return;
	}
	
	echo '<p>This is where you will put the tracking info for the package for ', $order->get_formatted_billing_full_name(),'.</p>';
}