Good Morning, Alex,

I've never encountered any problems with re-freezing partially full boxes of sheet film. I do try to have the film in a low-humidity environment for some hours prior to putting it back in the freezer. During either heating or AC seasons, that's easy. I use Ziplock bags, too. All that may be, as Ole's message suggests, overkill. Going from an extremely hot, humid environment directly to the freezer seems to be asking for trouble, but, otherwise, you shouldn't have any problem.