Agree with EMH here. It's going to depend a lot on your command, but the rules are pretty clear on this.
If you're going to be more than 100 miles (I think that's the limit) from your home location, you need to use leave. You get 30 days/year.
If you're going to continue to do work from the Guard while away from your location, you can try to get TDY. This is what could be done for doing audition rotations in other locations in the U.S. (and in many cases, your command may not even require you do that).
If you're going to go outside the U.S. it's going to get stickier and you're probably going to have to use up your leave. Also keep in mind that technically if you don't use leave during your Christmas/Spring break, your command can ask you to come in and do recruiting duties (our command tossed that out there to us).
If study abroad during med school is an absolute must for you, get it in writing before joining. If it's a nice-to-have, you could probably be comfortable something could be worked out.
As a note: I'd be very careful about getting new orders cut that take you off ASR. If there are funding changes, it might be sticky getting new orders cut putting you back on.