Just pick a good spot you want it to break and snap it off like you'd break one of those big size pretzels. The only part of the coral that's living is the tops of the polyps. If you want any more precision, any pair of pliers will do. Just grab firmly and twist the pliers.
I've fragged countless candy canes for the swaps this way. You pretty much can't kill this coral. The only ones I've ever had die were ones that fell behind rocks into the sand or RTN.