There is a very easy way to deal with this.
Modified and unmodified.
In the unmodified class,
The rifle will have to be as it came out of the box, no hamsters or but hooks. All Steyrs, AR20's walthers, Panthers are all delivered with the hamsters not attached. The minute you attach it, you have modified the basic rifle.
The same with cheek pieces, They all come in the lowered position, so to shoot unmodified, that is where they stay.
The Modified class,
Go for aftermarket stocks, raised cheek pieces etc, you can then choose to allow or ban but hooks etc.
Somehow I made TEAM ENGLAND 2012 and 2013
Illiterate writer for AirGunner
The real Kung Foo Panda.