ok to shorten a original drum track and add mixes to it?

Does anyone know if its ok to shorten someone's original drum sequence then add my own mix(es) to the shortened version?

I ask because I have some tracks that I recorded for only 2:30 ish of an original 3:00 track and do not need the extra time.

sure, shortening or lenghtening template tracks is within the "OK" range of mixing I'd say :) Its been done, the only thing we're picky about is that all involved musicians get their credit :)
Go ahead!