Last year, concerned that their super-hero pictures were becoming too dark and violent, Warner leaders assigned fan-favorite comic-book writer Geoff Johns and production executive Jon Berg to oversee the DC movie slate and give it a more optimistic tone. Their first task was a last-minute rewrite of “Justice League,” done with the “Batman v Superman” team of Zack Snyder and screenwriter Chris Terrio, to make the movie less serious and more hopeful.
Mr. Tsujihara also made clear he wanted “Justice League” to be under two hours, said a person close to the movie. “Batman v Superman,” by contrast, ran 151 minutes.