$phrase = $arResult["IPROPERTY_VALUES"]["SECTION_META_TITLE"];
$part = "#CITY_NAME#";
$city = "В москве";
$newphrase = str_replace($part , $city , $phrase);
if($_SERVER["HTTP_HOST"] == "msk.test.ru"){
$arResult["IPROPERTY_VALUES"]["SECTION_META_TITLE"] = $newphrase;
}