If your corals are attatched and are spreading on existing rocks, it can sometimes be a bit tricky to add more rock to the existing aquascape (i would imagine) I think it's basically like putting pieces of a puzzle together. In your case, a little fragging here and there, and you can do whatever you'd like with your rock work.

You can either remove the corals from the rocks they are on right now, or just life them up and put new rocks under them.

I would suggest taking all your rocks out, then remove the easy-to-remove corals, and aquascaping the whole tank at once to get the look you want.