Change the description for the optional groups on an Classic event page.

event_change_optional_group_header.html

<script type="text/javascript">
(function($) {
  $(document).ready(function() {
    if (window.location.href.indexOf('event_KEY=89503') != -1) {
      var e = $('#regForm2 > strong:nth-child(21)');
      if (e.length > 0) {
        e.html('Add me to the email subscriptions below to be notified of important alerts:');
      }
    }
  });
})(jQuery);
</script>