Since this is my first mapping contest here, I need some clarification regarding the use of textures and shaders.

1. Is it allowed to use all existing textures and/or shaders (including the ones created by contractors)?
2. Is it allowed to manipulate existing textures and/or shaders to create variations (including the ones created by contractors)?

I'm just asking to make sure I don't violate any licenses or rules by using/editing existing content. I'm currently planning to create my own set of textures and shaders, but in case I find something in the packages that fits my theme or decide to only use existing content in the end, it would be good to know the answers to these questions.

You can use them, just be careful that you aren't going against their copyrights if you are including those files in your map download. If the shaders/textures are already included in quakelive or quake3 then you don't need to worry about including them since they are already in the main pk3 files.

Treat it like you were working for a real company; you would want to avoid any kind of legal issue that might possibly arise.

That's why I asked.

Thanks for the answer!