from my experience people are given the elements of the track, if its any further than that in contract of gentlemans agreement then you stick to that. but i have heard many mixes that dont sound at all like the origional, but who cares. even that artist/label has got the rmixers in for a reason - to sound like them cos they're shit hot!!! if they do something crazy and different then so be it. sometimes people will ask for a few different versions to choose, or will ask them to do it again if they reject it, but thats mostly, again, either contractual or agreement.

i'd personally totally change a remix but make sure i did a killer job that would still sell to both my fans and theirs. cant ask more than that really can you?!