Custom changes when changing pro-sites level

I am using pro-sites and and I have modified the function - email_notification($blog_id, $action, $email = false) in pro-sites.php

I only want my script to run when a payment is actually made. So my question is, in the following code, I know that $action = 'success' on a first time payment, but will $action = 'receipt' on a recurring monthly payment? I also realize that tapping into the core pro-sites.php file is probably not a good idea. Does anyone have any other solutions for doing this?

function email_notification($blog_id, $action, $email = false) {
	  global $wpdb;

		if (!$email)
			$email = get_blog_option($blog_id, 'admin_email');

		<!-- My Code -->
             if ($action == 'success' || $action == 'receipt') {
			$level_result = $this->get_level($blog_id);
			require_once (ABSPATH .'/user_update.php');
               <!-- End My Code -->
	  if ($action == 'success') {

      $message = str_replace( 'LEVEL', $this->get_level_setting($this->get_level($blog_id), 'name'), $this->get_setting('success_msg') );
			$message = str_replace( 'SITEURL', get_site_url( $blog_id ), $message );
			$message = str_replace( 'SITENAME', get_blog_option($blog_id, 'blogname'), $message );

	    wp_mail( $email, $this->get_setting('success_subject'), $message );

	    $this->log_action( $blog_id, sprintf(__('Signup success email sent to %s', 'psts'), $email) );

	  } else if ($action == 'receipt') {............