I think culture is one of the hardest things to change, especially because the people who are controlling the culture are the ones at the top who have been there for decades. They have been socialized in this way of doing things. So I think getting leadership to buy in is absolutely essential. You have to have leadership who will not only talk the talk, but walk the walk and send a strong signal.
I also am a fervent believer that once you have the rules in place, you have to enforce them. I'm coming to believe that culture follows enforcement. It's a bit like seat belts. There was a time when nobody wore seat belts. Then it was against the law, and eventually people conformed.