LeonidS I've tried your code without parsing the GET request. Unfortunately, it didn't work with a simple string 'testing the new title'. 

<?php
require_once('./inc/header.inc.php');
require_once(BX_DIRECTORY_PATH_INC . "design.inc.php");
$_GET['i'] = 'search-keyword';
$oPage = BxDolPage::getObjectInstanceByURI('', false, true);
if ($oPage) { 
$oTemplate = BxDolTemplate::getInstance(); 
$oTemplate->setPageHeader('testing the new title'); 
$oPage->displayPage($oTemplate);
} else {
$oTemplate = BxDolTemplate::getInstance();
$oTemplate->displayPageNotFound();}