The burst disk function is down on the face of the fitting. Trimming off the top will not affect it's function. The thing you have to worry about is taking too much off and not being able to get the blown assembly out.
Ninja or someone had a burst disk holder that used an allen key. Maybe that's on a Raptor Rex? If you could find that fitting and the old two piece CO2 disk that matches, you would have a flush fitting. Did you check with Guerrilla? An allen key assembly sounds reasonable (someone should be making one).
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