ISAF Q&A2013-036 N005 states in Answer 4: 'Class rules are not racing rules.'

Question 1

Is 'racing rules' (as the term is used in rule 86) limited to mean only the rules in the current version of The Racing Rules of Sailing?
 

Yes, in general. Racing rules as used and specified in rule 86 means all rules in the Racing Rules of Sailing, including the Definition, Race Signals, Introduction, preambles and the rules of relevant appendices, but not titles, see definition Rule (a), it also means also ISAF Regulations 19, Eligibility Code; Regulation 20, Advertising Code; Regulation 21, Anti-Doping Code and Regulation 22, Sailor Classification Code, see Definition Rule (b).

Question 2

If the answer to Question 1 is 'Yes', may a notice of race change a provision of e.g. The Offshore Special Regulations or other documents that governs an event (provided the change is not prohibited by the document itself)?

Answer 2

Yes, the notice of race may change a provision or other documents that governs an event. However, when a document (such as the Offshore Special Regulations) is made applicable by a class rule, then rule 87 applies.