I could be wrong, but I believe they will use the keyboard that matches what specifically came with your computer for warranty reasons. So if your computer originally was built with the US keyboard, that's the keyboard it will get.
I would call Apple Customer service to ask this question, as the in-store Genius Bar employees will not likely be able to answer this question. And bear in mind if they are able to take special requests for certain keyboards, it may require longer time for them to have a keyboard shipped in for the special request.
This will be a custom process. They can do it and it will not cost them more but they are not obligated to, it will fully depend on specific employee mood and willingness to help, nothing else. So be gentle, be ready for a "no" but worth asking.
P. S. Considering your nickname - if you're in Russia and the laptop is sourced from the US with the regular US layout - from experience I doubt they'll help you. But still worth asking.