I can't think of any reason you couldn't do it. Shelf life should be good but not as good as if you left them unopened. This is assuming they're pasteurized/sterilized to begin with. You could probably get pretty good life by vacuum sealing them (again, not as long as they originally had). I wouldn't worry about them spoiling within a few months.

When you repackage some bacteria will get in that can lead to spoilage. However, the AW (water activity) will be very, very low in freeze dried food.

This might sound kind of nutty but if you have a decently stocked "modernist kitchen" you could use a vac sealer (preferably a chamber vac machine) to seal them, then sous vide the bags to pasteurize them. I would think that should extend the shelf life even further.