If you thought this out and really want to get out of of the MD program, ask the school about this. I'm sure each school has slightly different policies about dropping out of one half a joint program. There is not general 'rule' on how this is done. Ask your school.
If you are in it for the money, then this is a pretty bad time to be going into business with the recession expected to last for a while. I'm sure you have your reasons, but clinical rotations is NOT a waste of time. It's how you figure out which path is a good fit for you. Do you have academic difficulties? You should seek help if you are indeed struggling. Many schools offer tutors free of charge.