I'm not sure how, there don't seem to be any options to manipulate.
I went Data -> Terrain Cliffs -> BelShir Organic Cliffs, but there are no options to change.
Another question: Why can I add rocks and some other objects to the lowest level of my map (the level thats not accessible), but not temple statues, trees or wrecks. There are tons of each on SoW, but it always displays a red colored cursor and gives a error sound whenever I try adding anything.
I might need to write up a FAQ specifically for this reason. ICM just asked 4 out of the 5 most common questions ever about terraining and he's definitely not the first. I'll redirect you to my tutorial for now for more info, ICM - all questions you just asked are answered in there, so I'm sure your next 2-3 questions will be too.