WooCommerce add shipping method to emails

functions.php

<?php
// Place the following code in your theme's functions.php file to add the shipping method to all emails
add_action( 'woocommerce_email_after_order_table', 'wc_add_shipping_method_to_emails', 15, 2 );
function wc_add_shipping_method_to_emails( $order, $is_admin_email ) {
    echo '<p><strong>Shipping Method:</strong> ' . $order->get_shipping_method() . '</p>';
}
 
// Place the following code in your theme's functions.php file to add the shipping methid to admin emails only
add_action( 'woocommerce_email_after_order_table', 'wc_add_shipping_method_to_admin_emails', 15, 2 );
function wc_add_shipping_method_to_admin_emails( $order, $is_admin_email ) {
    if ( $is_admin_email ) {
        echo '<p><strong>Shipping Method:</strong> ' . $order->get_shipping_method() . '</p>';
    }
}
?>

I was wondering how this could be added as a separate plugin so that if the theme is updated it does not get wiped away.

I was wondering how this could be added as a separate plugin so that if the theme is updated it does not get wiped away.

You can use code snippets plugin and add this into there, so it doesn't get wiped away.