I have a simple question.

I have a music beat I really like, but the problem is it only lasts 50 seconds (either by design, or because I don't have the full beat, and I can't find it.. if I could find it I'd even pay for it..).

I'd really like to lengthen the beat, but not just by repeating it over and over again. I thought there may be a software that can repeat the beat and add to it some changes so that it doesn't get boring, but changes all the time, obviously having the same skeleton / basis of the beat.