Yes, you can remove the shaders or modify rendering settings in "/media/shaders/". What exactly do you want to change? There is basic assets that based for texture generation and you can modify them easy in /media/pa/terrain/. Sun is not some texture, but shader (sun.fs, sun.vs) so it's generated on the fly using Perlin noise. If you know GLSL well enough you can replace it by any other code.
