Hey, wanted to chime in

You _should_ be fine. I've changed ROMs a few times with no problems.
All the characters are tied to the phone via a unique device ID (hardware), similar, but not actually an IMEI (some devices in the future won't actually be phones, but laptops/tablets/etc, and won't have IMEI's).
That being said, I _think_ there are ROMs that allow you to change your hardware ID. I'm not sure why this is available, or useful, but if that gets changed you won't have access to your characters anymore. Normal ROM switches should be fine
