Having Terry Gilliam as director would be something they'd disagree with. And as I don't see Rowling as the type to hold off on production because of minor quibbles, unlike some authors.
Imagine if Rowling had asked to say directly that Dumbledore was gay. WB would kindly tell her no, and she would go count her money.
The thing is, the first HP movie was expected to be a huge blockbuster. And giving it to an eccentric like Gilliam, a man who, while a talented director, never makes anything with mass market appeal, simply would not make sense to anyone in WB.