If its not attached to anything large, All you need is a dremel and a diamond-coated attachment/cutter and slice away. Whether the tips of the polyps or through them its not all that bad. Make sure to wear goggles and a mask to cover your nose and mouth.
I was nervous too but after getting all these half-polyp acans then growing to full polyps i realized these are tough critters. I was right. acans are very forgiving when it comes to fragging. I fragged my favia/favites colony too in the same manner last week and they are doing great.