Keeping the existing player box is necessary for player movement (walking and jumping and such). I don't think having 2 boxes is going to have a significant impact. It's not like you're going to be able to hit somebody 10 feet away from where they actually are. Keeping the existing box will probably just extend the hitable area a few inches in front of what's visible.
Even if I can remove the existing hitbox, the problem of shooting through players won't be be solved. The additional box is necessary to bridge the gap between frames, since the server only runs at 10fps.
rafalluz: My point was that "quickly adapting" is not a skill this community is known for. People flip out over the smallest changes.