Changes go a bit deeper than just rule 87.

Start with rules 85 and 86.

In theory, class rules should only cover the equipment and no other aspect of racing (like course types). Some classes have sections in their bylaws or class rules that cover conduct of their major events (Thistle and Tornado classes come to mind), but whether these rank as "class rules" is subject to debate.

The RRS and World Sailing Regulations cover pretty much everything else. Sailing Instructions (and now the NOR, a change for 2017) can change only a very few rules, and only class rules as permitted under rule 87.

Note that for a World Sailing International Class (F-18, Hobie 16, etc.) approval of a class rule change not already permitted in the class rule must come from World Sailing, not the class.