You can cut a piece off, or cut the whole thing off, whatever suits you most.
However, I NEVER cut my xenia.
I keep rock rubble around so that as the xenia grows, I place the xenia up against the pieces I want to remove and they will climb up onto the rubble. Then it's merely a case of removing the rubble to wherever I want the xenia, or, in my case, I sell all I grow to one of the LFS's here. This method does not leave any residue to grow another from the spot it removed itself from.
It is easly to do this because xenia want's to always go upwards towards the light, so with the rubble next to it and higher than where it is based presently, it instinctively climbs up onto the higher piece of rubble.
If you don't want your xenia to spread, make sure it is on a high point, with downward slopes all around, and nothing close enough for it to contact outwards as it grows larger, as I have never seen it move downward in the years I've been raising this weed.
I wish I could make as much money with the weeds in my lawn.
