So a while back i came across people who could modify there appearance in game

i seen pictures of it
but as far i know its client sided and not visible to other people and its undetectable from whats been told to me.

is stuff like that against the terms or not?
like does it go with the same rules as how Shaders and Sweet FX are accepted
use at own risk etc?

also since it client sided people don't see the change to your character so it doesn't really harm the gameplay

i just wanted some clarification on this subject