The addendum is really very simple: To quote someone who already quoted the OP, so that the second quote cannot change the first quote, and can if fact be quoted themselves, unless of course the first quote is part of a multi-quote. If that quote is in fact, part of a multi-quote, but not quoted in its entirety, then the first quoter must agree to provide the multi-quoter the ability to use the modified quote in any subsequent quotes. All of this must be approved by the Tag Fairy, and that post must be quoted prior to any multi-quotes of any poster that was previously posted on any thread.
Unless of course the thread is not about the first rule.
Cheesburger?