They are out every night anyways, no real harm by moving the rock out and chiseling it off, or scrubbing it....
The coral will be fine so long as it stays damp....
Just put the rock in a bucket or bin... you will be suprised the amount of critters that are going to come runnning out of that rock... I found like a 15" bristle worm in one of mine, Never saw him in the tank but he came running out of the rock shortly after leaving it out...
Just remember to wear your standard gear, goggles and gloves.... dont touch the bristle worms with your bare hands or skin... you wont like it later.