(b) Sailing instructions may change a racing rule, but not rule 76.1, Appendix F, or a rule listed in rule 86.1(a). However, the sailing
instructions may change to ‘two’ or ‘four’ the number of
hull lengths determining the zone around marks, provided that
the number is the same for all marks and all boats using those
marks. If the sailing instructions change a rule or that definition,
they shall refer specifically to the rule or definition and
state the change.