Oh OK, because I tough that Lucas X Bayonetta was going to work because this mode swap was so funny but the 3ds and Wii U versions of smash are different. But putting the animcmd files of wario man over wario plus using a save editor for a custom part with +999 everywhere is hilarious and opA good 70% or so of all the model swaps won't work (crashing and whatnot), and even so most of them involve glitchy physics of some kind or crashing in certain circumstances. For a stable model swap, I've found mario over olimar and megaman over lucas to be pretty stable (Ive never crashed with them), while zsuit samus is HILARIOUS over Bowser, but crashes if you go into your shell (UpSpecial, DownSmash, etc.)
Things like that; you can't really tell until you try.