I have accepted a job starting late this year, but may be about to receive another offer much sooner. I definitely want to do the later one, how bad would it be to accept the first then leave?

I have already been offered and officially accepted a gig which represents a continuation of a move towards work in a new sub-field for me that I really want to move in to, but it's just a short term contract like the many I've been doing over the years and afterwards I'll have to return to scrounging for the next gig after that with no guarantee of further success in that area (except hopefully doing well and getting more offers but nothing concrete). This gig won't start for a long time so I need to start filling the intervening time.

I recently interviewed for another gig, which would be full time indefinitely, no more scrounging. It's a pretty great opportunity too, lots to like, but would likely represent an entrenching of my existing career path thus far rather than the move to the new one I've been embracing. Had this opportunity come up maybe a year ago I'd have grabbed it with both hands as I hadn't considered this other path but now I've begun on that new path I want to see where it can go. I think I did well in the interview and have a feeling I may be offered this full time job (not counting my chickens yet but it looks promising). That would be tricky though, the short duration, later-in-the-year gig will stretch just over 2 calendar months and I can't imagine getting that much time off from a brand new full time job in order to do the other one.

It's a small town with a small industry, and it's a damn shame the timing couldn't have been reversed. If I were to accept the full time gig until shortly before the 2nd gig later this year and then leave to go do this short term but arguably more interesting contract job, is it likely to go over so badly that I'd get a bad rep locally for this? I could cancel the short term job but deep down I'm pretty sure it's the work I'd like to start doing going forward. I could decline an offer for the full time gig if presented with it, but I have nothing else going and should really take on some work. It's unfortunate that I likely wouldn't be able to just walk back in to the first gig any time soon if I left and I'd probably appear pretty unreliable to them anyway having done so.