haha... that`s totally sounds like me
Yeah, faceplate is just the braket use to secure your card and hold any output ports so as long as you only trim faceplate it self it`s fine.
However I strongly recommend you remove faceplate of the card before trimming anything no matter what tool you are using.
That`s to avoid any grain of cut off metal to go on your card pcb.
Also before you fit faceplate back make sure you clean it properly for the same reason mention above.
Hope that make sense