Thus far every Smash game has been cracked open and heavily modified 64 - Sm4sh. Ultimate, however, has little to zero current modding support for a variety of reasons.. the game still being new and the console its on fairly young probably being the biggest reasons.
It'll likely be 1-2+ years before the modding scene picks up enough to do these kinds of things, and even then it may not happen. A big part of what fueled the modding scene for Brawl (which was huge) was the state Brawl was in. Ultimate is an amazing title from a casual AND competitive view point, so it'll probably have a LOT less people wanting to alter it, especially considering it's getting patches + new DLC characters in the future. The game isn't even officially 'finished', so I wouldn't hold my breath for big modding changes / support any time soon.