Would it be possible to switch to a branch like aviation or Medical Service later in my career as opposed to straight out of West Point?

Absolutely, despite being a ring-knocker!

Yes, it is possible, but the needs of the service always take priority. I have known line officers who became Medical Service Corps officers. I really can't speak for other designators as I was MSC (2300).

Damn fine question. It's an important consideration for those just beginning their careers. Inasmuch as others have already answered it, no reason for me to pile on. I just wanted to thank you for asking it. Most others haven't even considered it and it is important to them as well.