The plugin looks great and is what I have been looking for.
One question tho, are the assets fixed or can one use other assets?
Viewing post in Godot Nature Assets & Terrain Tools Collection comments
You can bring your own assets in to the pack. I am planning on building a tutorial and some templates in future versions, but for now, You can use the terrain materials for your terrain meshes as is. if you want materials to be working with the vegetation, you might need a bit of a setup and correct UVs. If you want to add your assets into the scatter tools, you have to update paths (I recommend duplicating the tool to a new one for your assets) pointing where your assets are.
Scatter tools which generate multimesh instances need a separate mesh resource (tres or mesh) so they can work properly.