You have to remove it from the wall. MAYBE, you can get away with pulling it away from the wall a bit. You'll have to figure out how far so you don't damage some OTHER part of the wall when you do the cut. If you do it this way, be SURE you block the back side of the molding so it doesn't move when you work in it. When you're finished, just pull out the block. (Kinda like what you'd do if you were working on your car that's parked on a hill. You don't want it to roll away, eh?) Oh, and be SURE you work the molding away from the wall a little at a time along the ENTIRE length of the molding. If you don't, you may split it.
I'm assuming you know how to finish off the end, right?
My best to ya and hope this helps.
Jay J -Moderator