I changed my system a couple of weeks ago with no adverse effects. I just logged in as admin, selected, server configuration and worked through to the end.
Originally rubbish.mydomain.com finished as rubbish.mydomain.local.
Good practic would dictate a backup just in case. I didnt need it and the whole process took less than 5 minutes. User accounts, ibays etc were unchanged and undamaged.
HTH
Peter