[Sil]

Load up the quarry mill mesh, then in the editor create a new mesh (with a new name would be best) while the old one's loaded. It should record the new triangles while the old ones are still there and you can link up quarry mill and the the existing mesh for the area - basically appending new mesh to the existing one. Don't forget to save it once it is all linked, and then load the new mesh before you start botting.

I have only done this with custom meshes I've made for mining so far and it has worked, so it should also work for the supplied meshes too.