Direct copy/paste from the official PlaneShift Player Guide.
\"Modifications to the client content (graphics, sounds, ...) are not allowed by PS License. In particular we will not tolerate players using mods to connect to an official server if those allow cheating, or modify the visual aspects of the game or its design. If you want to add levels or graphics to PlaneShift you are more then welcome to participate in our development.\"
Is this what you guys are talking about?