Adding: I ended up getting the shell off but ended up breaking off a small piece which I'm guessing was securing the front and back shells together. The trigger buttons and pieces remained intact on one of my two controllers which is what I was worried about, though I did have to fit the small trigger pieces back in.

The one controller seemed to fit back together just fine without the small piece that broke off, and buttons seemed to feel and work fine too.

I have 2 controllers I'd like to fix, and both have at least one stripped screw in them. Any tips for removing them?