So I could be a SEAL corpsman and after I've done that for a while go to Med School?
Hispeed, take a look at MILPERSMAN 1212-010 concerning lateral transfers (
http://www.npc.navy.mil/ReferenceLi...nel/1200Classification/1200_1214/1212_010.htm).
In short, you would have to go through a lateral transfer board to go from a SEAL to Medical Corps designator. With that being said, and like a lot of other things within the military, the decision to ALLOW you to transfer will NOT be in your hands. In essence, the Special Warfare Community would have to agree to let you go and the Medical Corps community would have to agree to pick you up. The SPECWAR community might consider all the effort (time and $$$) to train and qualify you and might not want to give you up. I am not trying to put a damper, but realize that, ultimately, it will not be up to you and it is sometimes rolling the dice. So to answer your question, it is possible to lateral, but with the country actively engaged in GWOT and the need for SPECWAR folks, it might be hard to let you go.
If you intend to go Medical Corps, you probably should try it from USNA. Worst case scenario, should you become a SEAL, you could always put a package in -- if you don't get picked up, then you still remain in the SPECWAR community. I'm sure you could get eventually get a medical billet with one of the SEAL teams, should you go Medical Corps out of USNA.
Hope this makes some sense.
In general, the lateral transfer process is TOUGH, regardless of community.