Advanced terrain moddifications, possible ?

I hope some experts can help me on this... i tried all the way arround and can't find any sollution. My problem:

I want to modify the terrain ingame... and i am not talking in here about Permanent Crater deformation, as it's not applied to Cliffs. So, is it possible for example to Plateau, or bring the cliffs to the same level ingame (with triggers, or any other method possible) ? I have for example 2 corridors (with the high parts about 2 levels higher) and i want at a momment to destroy the corridors, and leave just a plateau area... Is it possible ? Please tell me it can be done. Pleaaaaaaase. o_O

Thank you in advance for answering

The closest thing would be to use elevators, and have them rise up to block the corridor. It might not look all that good, but at least it's doable.