I have pruned my fairytale castle cactus back cutting all of the deat parts off from last winter's freeze. It was about 80% dead but it seems to not mind the slightly harsh butchering.
Once I was done it was still about half the height and about a third the width. A few pieces also came off and have been planted in their own pots. I don't know if it will be as successful as the other cactus that my wife transplanted which is smaller than my thumb but has already decided to flower. I figured it would take more than that since all she did was put it on top of some dirt in a pot and leave it alone.
Fortunately not all plants are that hardy or I would never be able to get rid of some of the weeds in my yard.