Example of how to use the FHEE__Registrations_Admin_Page___get_orderby_for_registrations_query to filter the orderby arguments.

tw_ee_filter_get_orderby_for_registrations_query.php

<?php //Do not include the opening PHP tag if you alreayd have one


add_filter('FHEE__Registrations_Admin_Page___get_orderby_for_registrations_query', 'tw_ee_filter_get_orderby_for_registrations_query', 10, 2);
function tw_ee_filter_get_orderby_for_registrations_query($orderby, $req_params) {
   // If ordering by DTT_EVT_Start, don't also order by REG_ID
   if(isset($orderby['Event.Datetime.DTT_EVT_start'])) {
      unset($orderby['REG_ID']);
   }
   // Always return the filtered variable
   return $orderby;
}