Is it possible to switch reserve branches while still on contract? Example: Air Guard to Army Reserves?

SSgt Adam Nawoichik, your example was not just a switch of COMPOs, but a switch between services. If that's what you're asking, then the program is called an IST (Interservice Transfer).

ISTs generally have specific criteria they are looking for (for example, open only to medical personnel on active duty, etc) ... much like the "In/Out" programs for changing AFSC/MOS easily.

However, either way, if you're currently under contract, you'll have to get a conditional release from your current branch before you can.

You'll have to see a recruiter to get a read on "how easy" it will be. It's 'possible', but by no means a given.