You'll need someone from Garmin to answer this for sure, but given how they are implemented (as enumerators), I'd expect that they will not change. If they were going to vary for any reason, I'd expect them to be functions or public variables in the module.
MOVE_BAR_LEVEL_MIN is currently 0, and MOVE_BAR_LEVEL_MAX is currently 5. These probably won't change since they're based on the move bar UI (and the underlying API) we have on some of our devices (e.g. the vivofit, which has a segmented LCD move bar).
