I purchased a torch coral a while back. When I took it home and introduced it to my system, I noticed a barnacle in the middle of one the heads of the torch. Apparently it is not entirely out of the ordinary for this to occur, as many Euphyllia encounter this. I left it there for a month or two, with no detriment to the torch coral. Now it isn't even alive... it just died, and all that is left is the hole thing. My torch has also grown a new head since.
I've heard though, that if you want to get rid of it, go to the tank at night (when the coral is entirely receded), take a paperclip, and just stab the barnacle a couple times. Again, this is only something I've heard you can do - as for whether or not it works, I can't say. HTH