It's just as hard as the first time around, if not harder. That's assuming that the Navy lets you #1 reapply for residency after only 2 years as a flight surgeon and #2 that they give you a re-deferment for the civilian match. Remember that although 2 years is the minimum time before you're allowed to apply to the Board, there's absolutely no guarantee that they're going to approve your return to residency...unless it benefits them. Then you'll either have to enter the NRMP match and plan on repeating your internship or scrounge around to find a 2nd year spot where someone left an opening. All of these steps can be potential stumbling blocks.
The logistics of applying to the GME Board, entering the NRMP Match (if allowed), and then separating from the military in the middle of your commitment can be very difficult while maintaining your clinical/operational duties. Imagine how much fun I had trying to arrange my separation and the movement of my household goods while deployed to the desert a few months before I entered my civilian residency.
I've proven that it can be done, but it took a lot of help from my Commander, his support staff, and my loving wife. This is all USAF experience, but I imagine the Navy is similar in this regard.
