What if Red Bull were approached and declined because they felt it was against the rules, and then later (say around June 20th) they discovered that it was within the rules and that Ross Brawn had found another loophole, like he had in 2009 with the double diffuser?
Let's not forget, RB spotted the double diffuser loophole the previous season and alerted the other teams, suggesting that the rules might want changing to close it. No-one was interested, he exploited it and the rest is history.