Hook to change the Success message after CiviCRM submits a form?
Xavier's answer is generally right but because you are in the context of a form I advise don't use the function CRM_Utils_System::redirect because that is a rather blunt instrument, and breaks pop-ups and other ajax-based forms (which don't follow the normal round-trip webpage lifecycle). Instead from your hook you can call CRM_Core_Session::singleton()-&gt;pushUserContext($urlYouWant); and the form controller will take care of doing the actual redirect or other appropriate action.

So from your hook you'd do:

$url = CRM_Utils_System::url('civicrm/my/path', 'argumet=1');
CRM_Core_Session::singleton()-&gt;pushUserContext($url);
CRM_Core_Session::setStatus(ts('Your foo has been barred'), ts('Saved'), 'success');