Does unanimously mean the rules were cast into stone? Manufacturers change stuff, conditions change, etc. Were the rules writers all seeing where their final submission for a vote addressed every contingency possible for the life of the boat?

Any set of laws or rules is a best guess to cover the conditions when they were written. The IWCA does, per its constitution, recognize that there can be changes. Specifically:

4. Meetings:
[...]
vii. New Business.
1. New motions.
2. Vote on rule or bylaw changes.

v. Rules Chairman
1. Be responsible for keeping the class rules current and organize any proposed rule changes.
[...]
4. Monitor class rules and recommend changes to the committee

So, let the petitioners for a tiller extension state their case, work through through the process, and put it to a vote.