I've got the same problem with my pink xenia.
If you want to just open up some room in your xenia patches you can place some rubble rock in them.
Ater about a week or two the surrounding xenia will have attached to the rubble.
Carefully pick-up the rubble and peel off from the main colony any stalks that are attached to the rubble.
If you want to remove some specific stalks of xenia just peel them off the rocks using a credit card or razor blade.
(I use a bamboo chopstick that I've carved down the end into a little "spatula" shape.)
Any removed loose stalks can either be placed on some rubble rock in a low/no flow area of your tank to attach, or you can bag them and trade/sell/ship them unattached.
"Damsels are the yapping, ankle-biting chihuahuas of the ocean.
They have no concept of just how small and annoying they really are."