Last year while making Harry Potter and the Goblet of Fire, producer David Heyman discussed the process of making the movie, the changes that would have to be made, the rating of the movie, Order of the Phoenix, and also mentions that JK Rowling has spoken with Alan Rickman about his character, Snape. While this interview is from last year, it is nice to see what changes have taken place in the movie since then.
Heyman discusses Rowling's involvement in the process:
In terms of Jo, her involvement is this. We send her each draft of the script, and she is there as the best consultant you could ever ask for. I mean, we'll send her lyrics of the songs to make sure that we're not doing anything untowards or we will send her drafts of the screenplay, because inevitably you tweak a little bit within the script. Kids are aware of most things, but sometimes there are little things that pass by us. It's not so much changes within the story or the book itself that's the issue. The biggest issue is that you don't want to do anything that adversely affects Book 6 or 7. So that's why we send her the script. It's not for the approval of the structure of the screenplay. It's because I made a promise to her and it's something that is really important to me that we be true to her world and not affect her world adversely.