Oh screw it, I don't want to be involved in another argument.
if you are too scared to get in an arguement then just quit posting, don't go
"FINE IM LEAVING I DONT WANT TO ARGUE :**((("
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Brick textures were changed by replacing the files in Base/Data/Shapes. I clearly remember doing this and having them be changed for everyone else coming on.
Perhaps there was a mod or something that added client sided textures but I know that you could make server sided ones that everyone saw.
I'm sticking to my answer that it is not and was never possible. (Although server sided textures can be easily done.)