I think you'll be fine, they are tough. Just be sure to cut on the overgrowth and not the stalk. If you cut into the stalk and the Zooxanthella comes out they will die.
Wear gloves, eye protection, and an apron because some species are extremely toxic.
1. If the base rock is soft enough I like to chisel under the zoas with a dremel knife and once they come up you can use tweezers to pull it up and off the rock.
2. When you have the amount you want, cut the base skin that holds them. If you squeeze one a shot of water will come out so make sure your pets are not around, it could kill them if they got it in their mouth.
3. Use cyanoacrylate (super glue) to glue them to the new rock.
4. Use a turkey baster to wash off the frag which will also set the glue and it's ready.
I've just began to experiment with this but I've done 4 frags this way and they are all fine and this was after I accidently burned the colony with a salinity of 1.030. They all looked deflated and dead and I thought it wouldn't hurt to take a couple now and they all recovered fine.
