Adding a deck plate isn't a structural issue. But if you can get your hands in there well enough to cut it apart, then go that route. And then get the "swingarm" style sender. If you want to put the same kind back in, though, it seems like you're gonna need the deck plate for install anyways.
FYI... obviously avoid dropping cuttings into the tank - the pipe cutter will avoid that. BUT, you also have to avoid dropping the tube back into the tank as you cut it. So maybe use some good tape below your cut to hold onto the piece, just in case. Or... cut through ONLY about 3/4 of the way around and then maybe you can bend that part over... cut the next section 3/4... etc.