BTA's can be fragged, it's quite easy and I've done it a million times. DO NOT DO IT IN THE THE DT! Some videos on YouTube show people taking the anemone completely out of water which I absolutely would not recommend.
Here's how I've done it and have never lost one:
Take a tupperware container and fill with tank water. Keep in tank. Put anemone in the tupperware container. Take the container with the nem out of the tank so that the anemone is not out of the water. This is a very stressful thing that you're about to put it through and the less stress (keeping it out of water) the better. Grab your sharpest knife (I like using my husbands extremely expensive fillet knife). Place tip of knife in the mouth of the nem and slice down quickly. Do not be hesitant, you need a CLEAN CUT. Turn the nem around and slice the other side so that now the anemone is sliced completely in half. When you frag it, you MUST make sure that the mouth is equally divided. Fill another container with tank water and some vitamins. Quickly transfer the newly sliced nems into that water, give them a quick rinse and back in the tank they go. I always, ALWAYS add vitamins to my tank water when there is a newly fragged anemone in there and continue to add vitamins once a day for a week. You must be diligent about your water quality while the anemone is healing. Small 5-10% water changes every two days usually does great. I also highly recommend running carbon (ChemiPure) if you're planning on fragging anemones. There is a risk that they can die, if don't properly it is minimal, but, run the carbon just in case. Also, if powerheads are not covered, now is the time to cover them! Newly fragged anemones are more likely to balloon and float around the tank.
I do not recommend fragging more than in halves. I know people do quarters, but that is far more risky.
**If you have evil clownfish that are very aggressive with anemones like I do, you MUST keep an eye on they. If they start beating on the newly fragged anemone, you will most likely lose it. The only anemones that I've fragged and lost have been do to the female beating the snots out of it.
I have fragged the Magnifica and about 2/3 survive.
**Fragging anemones is smelly. If you have a weak stomach, or a weak wallet, pass.