You know this would be al fine and ‘logical’ but if I make a new terrain in a new world in say , world comp, I CAN sculpt below the terrain, but I can’t do that in my 2 yer old terrain project,so why ? What values are being used in my old project that prevents it, and what values are being used in new project that allows me to do so ? That is the strangness that makes no sense, as the same values in placement rotation and scale , in new project are the same exact ones in older project.
BUt ya ‘changing’ the vaues at the beginning is horse pucky (* again you didn’t design the system) because as evvvveryone knows, thats not always how design, art, works. Yes for sure, why they didn’t make this easier for artists and all others is beyond stupid. I, we, shouldn’t have to be sitting here ready and eager to make new ART, games, incredible they are at least to us and have to be held back by this crud 
Maybe I should post on new features, I will, maybe then finally somebody will address this.