changing from 220v to 120v


There are a pair of Bryston monoblocks I am interested in that are 220v. The dealer says he can change them to 120v before shipping. I know next to nothing about electricity. Is the conversion easy to do correctly and well? Or migth there be non-trivial issues involved?

thanks for your thoughts.
tanglewood
James Tanner, owner of Bryston, recommended not buying amps built for a different country. I am going to heed his advice.  I'm also worried the warranty might not transfer.

thanks for all the responses. 
I woulds never buy a 220v amp to be converted get 110v only it could be a problem.
it really depends on how a specific unit is built and whether it is internally configured with proper power transformers and circuitry to handle different input voltages - some are easy to do, made for quick-shift... others not so much

so i would lean on the manufacturer to advise on the wisdom of the input voltage swap