I have the same coral and it definately grows like a weed. You do not need to remove it from the tank but it will slime up a fair bit after it's cut so be sure to add a good grade of carbon for a few days afterwards.
If you go to the local craft store, you should be able to pick up some cheap plastic exacto blades like this one.
Perfect for soft coral fragging and cheap enough to toss when your done if they rust. Rinsing the blade and drying it well could preserve it for another use though.
Simpley find a clear area to slice through the coral stock and have at it. It sound harsh but it's quite simple and as long as your water specs are good the coral will recover in very short order. Be sure the cut is clean, do not tear and try to wear latex gloves. They can be a little hard to get a grip on.
Once fragged, you will also need a clear area in low flow where the frags
can be placed with rubble rock to attach. A shallow plastic food grade container with some veil material will work or a HOB
breader box with pleanty of extra holes drilled in it for water flow which is what I use. The frags
should attach in a week or two and then can be sold, traded or placed alternately in the tank.