Are you referring to NiceHash with the above comment?
I don't know if NiceHash offers the feature of switching pools partway through a rental (although I suspect they do - it's a pretty standard feature) but they do offer pointing to a pool of your choice, so you aren't stuck with mining straight bitcoin.
I do know though that MiningRigRentals and BetaRigs both allow renters to mine anything SHA-256 that they want, and allow renters to change pool configurations partway through a rental.