Just be reasonably careful handling and cutting. The plant is pretty tough and any minor damage done will die back a little and then regrow. Generally, the reason for turning the ball is to keep it round. I've always used pea-sized polished gravel on the bottom of my tanks, so the moss balls get oxygen on the bottom. If you want to keep some in a ball, just roll it regularly. I used to roll it when I did the weekly water change.
"Fear not, my young apprentice. Just change the tank water."