I can't really tell you in detail, but here's something that will help - make sure when you first remove the cellophane, that it stays entirely intact and the the folds remain still in place where possible (ie. don't rip it, and don't open it all up so that it becomes a flat piece of cellophane; after it's opened, if you just put it on a surface, it should revert mostly back to a rectangular prism shape with just one side opened. I'm a very pedantic person, and I always take care never to rip my cellophane wrappings. I have one here that is all in one piece, mostly still folded, and it would be just a matter of getting some adhesive of some sort (can't help you on which to use though, I'm sorry

) and sticking it back.
This for me is at least possible for D&D's Smoke and Mirror decks, they're wrapped nicely. I can't remember enough about the cellophane of other decks though - though I'd imagine that the same principles would apply wherever possible.