tbh i didnt understand your question very well! but i will explain what i did.

i created a layered texture in hypershade.
added the dirt (pressing the 2D textures / File and choosing the image)
then with right click in empty space created a green small icon where i applied the grass.
and then middle mouse button to connect it to the lambert

then i created 2 UV Sets (Dirt and Grass) did the nessesary changes in UV texture editor, linked them (grass to the lambert grass and drit to the lambert dirt) and voila i could use the Paint Vertex Color Tool in order to while i was erasing dirt , grass would show up .

i really hope this answers your question!