I'm looking to edit a ground texture and possibly also change the type of grass that it spawns, does anyone know any good tutorials for this are? (I know this can't be done in the CK, but this forum is where all the "mechanics and details of trying to make a mod" people go, as opposed to the mod forum which is more for releases, progress updates and ideas.

Bump.

http://www.youtube.com/watch?v=p02NysXwV5U

That should help. Essentially it's the same process.

How different would it be edit a texture but have it not replace any defaults? All the tutorials I've seen so far about textures are of just replacing existing ones, using the same name and etc. Or do you just have to give your edited texture a different name so it wont override anything?

Correct...just give it it's own unique name (texture set) and then when you attach it to the mesh, give that a unique name as well.