The tech
Your PC. Your POV.
Think of it as a stage costume. The match still knows who you are. Your machine just draws the look you picked.
On your PC
Galaxy Swapper rewrites the files Fortnite reads locally. Your Epic locker stays the same — that is why the squad is not wearing your new drip.
Owned slot → new look
You swap from something you already have. The whole lobby does not unlock Black Knight. You just look like it.
After a patch
New season, new files. Grab the fresh V2 build and swap again. Easy.
Is it a texture pack?
Closer to a real Fortnite skin changer than a Minecraft pack. Built for this game.
Consoles?
PC Windows. That is the whole map.