You're not going to be able to apply for both. You can apply for the legal program and go to law school, or you can apply for the flight program and go to flight school. The only way you could make that transition is to make a lat move after already serving in one of those fields for a time. It'd probably be easier to go from Aviation to Law, but that's just speculation. You can always ask to be the legal officer wherever you go, but there is no "I wanna star in J.A.G." MOS.