Just create dedicated no-paint layers for the different grasses.
Then you can mix them in the material like you would anything else.
Specificslly for removal, you make a grass layer with no meshes. Paint that on and the area will always not have meshes.
Geberally speaking you want to avoid having grash meshe and grass layer use the same landscape layer - at least until you get into optimization.
At that point you’d know better than to use landscapes anyways.