to NGA!
Some cactus lend themselves to being taken apart and re-rooting the pieces and some do not. Cactus that don't mind come apart easily on their own. Echinocactus oxygona and all the Prickly Pears come to mind. Anytime you have to use a knife to break apart a cactus, you are taking the risk of killing it.
I'm not sure what kind of cactus you have (maybe Mammillaria) but it is absolutely beautiful.
Instead of taking it apart, lift it to pot rim level (add soil underneath) and enjoy your fabulous looking plant.
Daisy
