Trimming mouthguard

[jmiami 4]

Hey all, I just received my custom Impact mouth-guard after biting into a mold and sending it to their lab. The fit on my actual teeth is impressive, but there are parts of the mouth-guard that feel extraneous.  The part that shoots up into the roof of my mouth, for instance, goes way too far back into my mouth.  It does not leave much room for my tongue to move around. My instinct is to find a way to trim off what ever I don't like, but how do I do this? Do I use scissors? Or a razor blade? Or a box-cutter?  I don't want to mutilate the mouth-guard while trying to customize it. Thoughts?

[Vet88 674]

Anything that cuts will do the job but scissors are the general tool used.