If you're using skins which are the same size as the normal ones that's totally fine. It's only not fine when you're using tiny skins because it changes your hitbox and damage taken becomes less since you're not taking hits in your screen.
Same goes for the vehicles modifications, you can't modify a big car into a small one because it gets bugged all the time, plus you can shoot through it in other player's screens since its big for them but small for you. Be careful with what mods you want to use.
Use whatever you want as long as it doesn't change the size or the shape completely
