Proccedural + Paint in one material

Hello everyone ! First of all my primary language is french, so I do the best I can, if something are not clear or not precise, just tell me.

I create a nice proccedural material for my landscape and I think I done something cool. Now I want the possibility to create road with a painting mode (vertex or landscape tools, whatever). But I dont find a way to get it.

When I try with the Vertex mode it’s always do nothing. Even if I try to use a material dedicated for Vertex paint. (It work on other object but never on landscape). So I deducts this. Landscape can’t have vertex paint. If you could help me on this subject, it would be appreciated.

The landscape paint tools do not work too with my material. Maybe It would help you to know how my material work.

I learn how to make it right there and it is the same except for the grass material function.

So if someone now how to make a proccedural + paint mode possible at the same time, it would be answome to know how! Thanks for your help and reading.