Generally they are very hardy. I'd cut it anyway that seemed to make sense, probably making sure to include a part of a finger that shows polyps on each frag.
Depending on the specific type of finger leather it may be a little bit tricky to mount. IME the tricky part is that if you have the frag pressed into, or tightly rubber banded onto a rock or frag plug, the frag may tear and or start to rot/get a bacterial infection where it is pressed up against the mounting surface.
What I've found works with any of the finger leathers I have kept is;
-find a piece of rubble that has a bit of a U shape, or a bit of a hole in it about the size of the base of the frag
-Stick a plastic toothpick through the base of the frag, not too close to the bottom, probably closer to the middle
-Fairly loosely attach the tooth pic with a rubber band so that the base of the frag sits in the hole or low spot on the mount, You want it sort of hovering, or just lightly touching. Secure it with the toothpick, but keep it so there is no real pressure on the frag
-Don't touch it until the rubber band falls off (because rubber bands don't last long in saltwater, but they last a little longer than it usually takes for a frag to attach itself)
