GSP is virtually indestructable. If you can get a fingernail, toothpick, credit card etc. under an edge, you may be able to peel the colony off - this is easy on flat surfaces like glass, sometimes very hard or impossible on really rough rock surfaces. When you've peeled back as much as you want to remove, just use a razor blade to cut the mat. You can re-attach the frag elsewhere or sell it, if you're gentle it should come off undamaged, and taking off a piece won't harm the rest of the colony whatsoever.