I have cut a few BTAs (quite a few) but I dont like to recommend it for fear that every newbie will be propagating their anemones to "re-coup their costs", and end up killing anemones.. Not that I have a lot of anemone experience, but I believe that only experienced hobbyists should attempt this.
they anemone needs to be very healthy to begin with, and needs to go into a very stable/healthy system after the cut.
Phil's post is dead on. If they are too large, they are hard to deal with.
If you have to peel the anemone off of the rock, you are starting the stress levels before you even cut, which IMO decreases you chances of success. If you can get to the anemone easily, then the chances are much much better.
I like to use a shallow container filled with tank water.. I use a 4" razor to cut directly across the mouth. After the cut, a few 100% water changes into the container over a period of time, discarding the old water and using water from the tank where the anemone came from. As Phil said, its best to have another system to put the anemone into, but NOT a NEWLY set up system . The system needs to be stable/established. I am sure that there are vids of Mr Calfo cutting anemones floating around out there somewhere..
The only anemone I would ever attempt to cut is a BTA. although I do give props to Phil for trying and sharing his efforts with the mert.
( BTW, I picked up./rescued another gigantea. It was bleached but seems to be doing very well. My purple has grown tremendously.. almost the size of my 14 year old male. The newest is olny about 5", the purple is about 16 and the old male is about 20")