Otherwise every dinghy with a trapeze would have to include some dispensationg in class rules.
Exactly so Peter. The RRS acquired this rather pointless bit of bureaucracy in Jan 2011. Its in 86.1c which from January will read "Class rules may change only racing rules 42, 49, 50, 51, 52, 53 and 54. Such changes shall refer specifically to the rule and state the change."
It will doubtless be many years before everyone gets round to doing it if even ISAF classes haven't caught up yet.