escaping the Client Email Header Content for specific email template

[m107]

I am trying to remove the Client Email Header Content for specific  email template.  The following hook code did not work:

<?php
add_hook('EmailPreSend', 1, function($vars) {
    // Check if the email being sent is the one with ID 12
    if ($vars['messagename'] == '12') {
        // Remove client header content
        $vars['body'] = preg_replace('/<!-- Client Header Start -->(.*?)<!-- Client Header End -->/s', '', $vars['body']);
    }

    return $vars;
});