I had one of the early Steyr Hunters and ordered it with a "Stabiliser" (the first ones didn't have them fitted) and a power adjuster (because I could).
It came with the silver port. It could not be adjusted over 12FPE. Unfortunately it wasn't very efficient and the shot count was in the region of 40/50 shots.
I drilled the port out to (I think) 4mm, which put the shot count back right up. I have covered the adjuster with an alloy piece to make it not directly accessible. You only need two allen keys though to adjust the power. To be fair, once set the power has not altered.
I understand where your coming from but I think there is little you can do about anything if you are unfortunate enough to have legal power issues. The chances are very remote but also serious if it's you.