[Paul M]

or if you want to use the datamanager, try this ;

if(is_member_of($vbulletin->userinfo, X))
{
	$thread =& datamanager_init('Thread', $vbulletin, ERRTYPE_SILENT, 'threadpost');
	$thread->set_existing($threadinfo);
	$thread->set('iconid', Y);
	$thread->save();
	unset($thread);
}