I've set myself a stupid task, that I didn't solve couple years back, again. I've got few meshes with normals pointing inside. Caves. Like mostly circular rooms and tunnels that should connect them. Making tunnels to connect to a room is not a problem, just have their sides open and make a connector that will hide connecting edges if there are some sort of artifacts. But what to do with rooms. I need to cut holes in random positions in walls.
Solution was to use Parabox CSG for boolean operations. But there was a problem. If I just take a box flip normals and try combining it with a room I'll get a recessions in walls, but not holes. And then I tried to remove one face of that flipped cube and positioned it inside that flipped dome mesh, so that they do not intersect.
And in result I had exactly what I was looking for. A clean mesh. Cubes material is not present in the result, nor any triangles.
I hope it will help those few that try to do similar things and fail to find any semi acceptable results. With this you can go full procedural and do anything you want.