Terrain reads

I have an existing terrain that I want to keep. I mean the mountains and such that I had to manually adjust to place a few things on it. But I want to auto generate the textures/grass/trees and so on. Can I do that with Mapmagic without losing my terrain?

https://forum.unity.com/threads/released-mapmagic-2-infinite-procedural-land-generator.875470/page-36#post-7736190