Trimming a holster. Good idea or horrible?

I've got a Glock 21 and Galco Jackass rig. I'm loving the beavertail, but it doesn't quite fit. I'm thinking that I could trim or Dremel out a sliver to make room since it's an extremely small amount to trim. Is this an awful idea? via /r/CCW https://ift.tt/2BHXckv