I switched programs after doing one and almost a half year of FP. The program was on probation and I was really lied to regarding the situation the program was in. They were very malignant. When I told them I wanted to leave and that there was a position available elsewhere they went ballistic. They consulted a law firm, threatened to sue for damages and really were inappropriate to the other PD that I was working with.
I'm still threatened with being sued (which by the way would be the first time a residency program sued for damages-which I've been told by my lawyer) and I occasionally still have to work with these rejects now that I'm in my new program-which by the way I love. I talked to my new PD and he said he's let people go mid-stream after the contract is signed and said he never imagined that a PD would act the way this other guy did.
My advice is to talk to them upfront, but do not expect them to be jumping up and down that you want to leave. After all, you have to remember that you are putting them in a bind as far as covering call and the other resident's have to bear more weight. On the other hand as I pointed out to my previous PD, why would they want someone there who isn't committed or motivated to their program.
My lawyer said no matter what, they can't force you to work in spite of signing a contract-that's forced labor and in America that's illegal. The problem will be if they fight and they might get other programs to turn you down. My advice is don't tell them where you're looking at going to (if you are thinking about changing programs) that way they can't put pressure on the other program.
Overall, it is not a pleasant process and you'll risk really pissing off some of your fellow residents and current PD. Just make sure that you can stand up to all the crap before you get the ball started.