How to change domain for a Facebook application

I have a facebook App which corresponds to one domain, so that users can use FB to login to oursite. Now, customer needs that domain to be changed. Is it possible just to change the domain in App configuration? what will happen with already registered users? I ask this because when I was developing the site, I used a development url. When site goes to production, I can not login by FB anymore. Maybe the number returned by FB has a link to the domain where the user has registered. Is it a way to modify this?

Regards, Jaime