[ozzy47]

That will work, but if you want to do it via a plugin, so you will be safe from upgrades, you can add a plugin.

ACP --> Plugins & Products --> Add New Plugin

Product: vBulletin
Hook Location: ajax_start
Title: Disable Double Click to Close/Lock Thread
Execution Order: 5
Plugin PHP Code:

if ($_POST['do'] == 'updatethreadopen')
{
	$vbulletin->input->clean_array_gpc('p', array(
		'threadid' => TYPE_UINT,
		'open'     => TYPE_BOOL,
	));
	if ($threadinfo['open'] == 10)
	{	// thread redirect
		exit;
	}
	//load the existing open status to return if no permission
	$open = $threadinfo['open'];
	// changed perms to disable doubleclick
	if (
		can_moderate($threadinfo['forumid'], 'canopenclose_not') // user is moderator
		OR
		(
			$threadinfo['postuserid'] == $vbulletin->userinfo['userid'] // user is thread first poster
			AND
			($forumperms = fetch_permissions($threadinfo['forumid'])) AND ($forumperms & $vbulletin->bf_ugp_forumpermissions['canopenclose_not']) // user has permission to open / close own threads
		)
	)
	{
		$open = $vbulletin->GPC['open'];

		$threaddata =& datamanager_init('Thread', $vbulletin, ERRTYPE_SILENT, 'threadpost');
		$threaddata->set_existing($threadinfo);
		$threaddata->set('open', $open); // note: mod logging will occur automatically
		if (!$threaddata->save())
		{
			// didn't change anything
			$open = !$open;
		}
	}

	$xml = new vB_AJAX_XML_Builder($vbulletin, 'text/xml');
	$xml->add_tag('status', $open ? 'open' : 'closed');
	$xml->print_xml();
}

This way you will be safe from overwriting it during upgrades, and if you ever run Suspect File Versions the file will not show up in the list as containing unexpected contents.