As far as I can tell, Apple won't do it. So be sure to get the right one before plunking down the cash. And you may have to resort to buying overseas from the appropriate online national store, since all I've seen do not carry all the possible keyboard combinations.
In days of yore, changing the keyboard was straightforward since it was just screwed on top of the topcase. With the unibodies, first the keyholes have to be right on the chassis (there are at least two different hole configurations). Then, the keyboard assembly is the first part that goes in. Meaning that you have to literally gut the Mac and take EVERYTHING out before reaching the part again. It is such a risky task that my two favorite DIY parts places (IFixIt and PowerBookMedic) won't even carry the replacement keyboards!
Here's a list of all the keyboards that Apple makes (click on the triangles to view the images):
http://support.apple.com/kb/HT2841