Changing Default Ground Texture

[Shaa]

After searching and googling I was able to get the ukts texture pack installed and using the info from "the Grade Crossing" was able to edit and make my own texture file. Now the one thing I haven't found is what I need to change to alter the default ground texture away from cajon passes scrub. I'm not sure what line I need to change or if it's even possible. I'd rather not have to paint the entire route with new grass.