I have fragged sinualria fingers off in the tank. It was too big to remove. I would just cut one or two arms at a time and then not touch it for a week or so. When I fragged my toadstool, I cut an inch off the whole outer edge so it made a donut with a big hole in the middle. I then cut that into smaller pieces. I let the mother colony set in a bucket for a few minute before placing it back into the tank.
It will depend on how much water you have in your system as well. A larger tank can handle these changes better. It is a good idea to run carbon afterwards as well if you don't normally.