Sometimes we just want a colony which is consistent in type of polyp and coloration for many reasons which is fine. I had this issue myself and here's what I do and it always works.
Wear reef safe gloves and eye protection as there will definitely be some possible squirting going on. Place the rock on a concrete floor or slab. Using a hammer and a 1/4" wide chissel. With light taps, scribe a line around the area or polyps to be remove. Be careful not to damage other polyps around the ones you want to remove, they will all retract anyway, which is good. Once you lay down your scribe line, with firm single or double taps, angle the chissel downward and inward slightly. The polyps will remain attached to small chips of rock which can be then glued to other crevice rocks and sold or given away.
Then place 5 drops of Lugols iodine in a bowl of water, it has medicinal properties, then dip both the mother colony and the frag briefly. It will aid in their recovery. Before replacing back in your tank, dip both rock in a bowl of tank water, then place on the substrate in line with current as some slimming may occur which is normal. The current will help remove said slim. Wait a few days, if the colony looks fine, then you can replace it on your reef and/or sell the frags you have now created.
I have done this dozens of times with no issues at all. Good luck.
Mucho Reef
