how do you change ground textures in ce, im pretty sure that its possible in guerilla but i honestly dont know

(sorry for ignorance)

Within the shader tags there are references to bitmap tags.

Compile your textures into .bitmap files, and open the file

LEVELS\TEST\BLOODGULCH\BLOODGULCH.SCENARIO_STRUCTURE_BSP

Scroll near the middle and you'll find references to shaders. Look for the shader_environment tag called Dirt.

Open that shader, and in the middle are the references to the bitmaps. Use the [...] button to browse to the bitmap tag you created, hit save, and compile your map in Tool using

Tool build-cache-file levels\test\bloodgulch\bloodgulch

Open Halo and check out your new texture.