Sailing Instructions can only change a class rule by stating the rule number and the change (RRS 86.1(b))
Except, doesn't ISAF Regulation 26.5(f) apply and restrict changing the class rules for the ISAF-recognized classes?
But since you guys rarely/never race Hobie One-Design, you don't have to worry about it.
I was always under the impression that if you race in an open event, you're supposed to follow your class rules. I know there are adjustments for equipment changes (adding a chute, etc.), but isn't there a general assumption that you will race your boat to its class rules?
I agree though, most likely, no one would ever protest you until after the racing, and usually only if they had something to gain. An OA might protest you depending on the level of the event, if there were on-water judges present, etc.
Mike