wcmo_new_registration_email_content.php

<?php
/**
 * Filter the content of the new user registration email
 * @param $message		The email content
 * @param $user 			The user object
 * @param $blogname 	The name of the site
 * @param $url				The url for the user profile
 */
function prefix_new_registration_email_content( $message, $user, $blogname, $url ) {

	$message = sprintf(
		'<p>%s</p>',
		'My new message goes here'
	);

	// Use the parameters to include extra information
	$message = sprintf(
		'<p>%s: <a href="%s">%s</a></p>',
		'Follow the link to review the user',
		$url,
		'Click here'
	);

	return $message;

}
add_filter( 'wcmo_new_registration_email_content', 'prefix_new_registration_email_content', 10, 4 );