I have a Moen shingle handle tub faucet that drips. It is installed on a fiberglass tub/shower. I am trying to replace the posi-temp cartrige but can not remove the clip because the plaster ground is in the way. I do not want to remove the plaster ground as the trim screws attach in to the plaster ground and forms a seal against the fiberglass wall. The plaster ground is behind the fiberglass tub wall, and the fiberglass wall hole is smaller than the plaster ground circumference. Is it OK to trim/cut the plaster ground enough so that the clip can come out, but the trim screws can attach to the plaster ground? If not, are there any recommendations as to how to deal with this situation? The components were installed at the time the house was built in 1995.