If you do not have possibility to use .htaccess files all your changes will not take effect.
You can try to ask administrator to perform such changes for you.
And as far as I see these settings (php_value) won’t be used on this hosting.
So you should better check how to set this options on your tariff plan.
(php.ini or so)
You can also use “bitrix server test” script to see if your system meets Bitrix products requirements or not.
Ask Bitrix’s Helpdesk for more assistance with script and some extra checks.
Also write to DH administrator with direct question about mbstring options.