I am not sure. I am unfamiliar with the consumer camera segment.
I have heard about some "firmware enhancements" like Magic Lantern or CHDK for Canon which, if I understand correctly, are some kind of extensions that could be loaded by the camera's main firmware on startup and then provide additional functionality.
It is not a custom firmware. But it offers similar functionality.
Its fun and it looks good, but if you ever want to migrate away from it you pretty much have style everything all over? You can't just change the style of a a single tag?
