cutting/modding a mask to give you cheek weld is not a problem, you can mod a steel mesh lower half mask with a pair of tinsnips and a hot glue gun. There's a youtube video of someone doing it. The problem comes when you remove too much material that it doesn't sit well on your face, you may need to find another way to secure it.
The major risk is dental damage, a welt or bleeder on the face is not the end of the world.
Depending on the gun of your choice though, it may or may not be as big an issue. The taller the sights are on a gun (height over bore) the less of a problem cheek weld is, but this complicates aiming as you have to keep in mind how tall your sight is off your BB target and how you sight in the gun with the hopup.
I futz with V2s, V3s and V6s. I could be wrong... but probably, most likely not, as far as I know.