Germain Lussier looks at how and why the upcoming Zootopia switched out its lead character late in production:

In Zootopia, which hits theaters March 4, a young bunny named Judy Hopps leaves home for a job as a police officer in the big city of the title. There, she must team up with a con-man fox named Nick Wilde to solve a crime. Nick, voiced by Jason Bateman, is jaded, sarcastic, and believes everyone is exactly who they are. Judy, voiced by Ginnifer Goodwin, is exactly the opposite. She’s cheery, optimistic and believes anyone can be whatever they want.

For years, Nick was the focus on the film, with Hopps playing a crucial, but secondary role. But on that fateful November day, a little over a year before the film’s release, director Byron Howard realized they had to make the switch.

In live-action films, the stages of writing, production and editing are distinct and sequential, so you rarely see this kind of major 11th-hour refocussing. By the time you realize you’ve made a fundamental mistake about your central character, you’re largely stuck with what you’ve shot.

Animation, on the other hand, is iterative. As you move from screenplay to storyboards to scratch reels, you see the story coming to life — and the problems front-and-center. At each step, you’re screening and debating and rewriting. Talk to animation folks and you’ll hear countless stories of sidekicks promoted to heroes, and whole plotlines ditched.

In our Scriptnotes episode with Jennifer Lee about Frozen, she described some of the major changes to Anna and Elsa while in production.

I’ve mostly worked in stop-motion animation, which falls in the middle between live-action and CG animation. For Corpse Bride and Frankenweenie, we had a lot of flexibility up until the shutter clicked. From that point forward, it was very difficult to make significant story changes, much like a non-animated movie.