We have users submit tickets from within a different application and wanted to use existing forms, so a redirect would be the best scenario for us. After a bit of searching, realized this simple solution wasn't in the MODS.
You will need to comment out 1 line and replace it in open.php-- its that simple! Go to line 34 & Look for ... //Thank the user and promise speedy resolution!)
in open.php, look for the following code:
$inc='thankyou.inc.php';
Comment out that line and replace with the following:
@header('Location: http://www.mydomain.com/thankyou.html');
//$inc='thankyou.inc.php';
That's it -- enjoy!