Adding an extension to Terrain Tools

I have an idea for an additional terrain brush but first I will explain why I need it. I have a terrain mesh made from drone photos of a forested quarry. The model looks great so long as you don't get too close. In reality every grass hump every bush and tree is just a mangled protrusion from the mesh. I have tried using 3DMax and Maya to smooth and cut it but that leads to other problems. As my final target is to use the quarry in Unity I thought I would try and emulate it with the existing terrain tools. However the brushes do not detect the height of the previously mentioned mesh and so it becomes a very tedious job to replicate the mesh in Unity Terrain. And so to my idea, what would it take to create a terrain brush of variable size that is an actual 3d object such as a sphere or cube or plain that could be scaled and then dragged over the surface of the preexisting mesh and have the Unity Terrain respond to it. The workflow would be, create a new terrain in Unity and import the mesh terrain and place it within the bounds of the unity terrain. Then using this brush I want to create drag it over the surface of the imported mesh and have the Unity Terrain rise to the same height as the mesh. Any suggestions or help would be appreciated and if any one wants to take this idea and create a product please feel free to do so. Also if anyone is familiar with Digital Elements Worldbuilder 3D it word be great to be able to replicate that method of creating terrains in Unity as well.