The file format is bfres when you extract via the szs file.
Use this to extact szs files
https://github.com/jam1garner/WiiUZip/releases/tag/v0.7
And for bfres you can do two things.
Texture editing
https://gbatemp.net/threads/release-bfres-texture-injector.422580/
Vertex edting
https://gbatemp.net/threads/alpha-bfres-vertex-tool-aka-most-nintendo-models.443529/
A nice WIP viewer (SMB made the branch, tool developed by Jam, Ploaj, and Y2K)
https://cdn.discordapp.com/attachments/203588032467566594/250236529270718464/Release.zip
Git repo of said tool
https://github.com/jam1garner/Smash-Forge
No model importing exists yet but hopefully soon.
This format is used in may games such as
(List by RTB)
Animal Crossing Plaza
Captain Toad: Treasure Tracker
Game & Wario
Kirby and the Rainbow Curse
The Legend of Zelda: Wind Waker HD
Mario Kart 8
Mario & Sonic at the Sochi 2014 Olympic Winter Games
Mario Tennis: Ultra Smash
New Super Mario Bros. U / New Super Luigi U
Nintendo Land
Pikmin 3
Pokémon Rumble U
Rodea: The Sky Soldier
Splatoon
Super Mario 3D World
Super Mario Maker
Tank! Tank! Tank!
Wii Sports Club
Wii U BIOS
Yoshi's Woolly World