I've seen a few guys cutting the triangular inner plastic out of their shockwave blade stabilizers and had some questions about it. I thought it looked cool and different from everyone else's so I was thinking about doing the same but don't want to get in trouble. I don't want to alter the design and then find myself in some kind of trouble with the ATF or something. I figure it's perfectly fine but figured I'd see what you all had to say. Also if anyone has some tips for cutting it out I'd appreciate them as well. Thanks

As long as your not shouldering I really don't think it would matter. Granted as is it is BATF approved technically once altered it probably is not approved (this doesn't mean it's illegal). It should not matter though. I am a hillbilly though so I don't know the facts or laws pertaining to something like this.

You're overthinking it.  All you're doing is cutting lightening holes.  You're not going shoulder it anyway, so the point is null.