I'd like to see a system whereby you could take a bridge officer candidate and make him a duty officer instead.
To keep it balanced I think when making such a change Boffs would have to get reduced one level in rarity: i.e. a rare (blue) bridge officer would become an uncommon (green) duty officer if transferred. Also you wouldn't know what characteristics the Doff would have although since these are based on race you would have a general idea of what they will end up with.
This makes sense to me because you seem to end up with a surplus of bridge officer candidates that seem rather worthless. From a thematic standpoint it also makes sense because ultimately bridge and duty officers are all just crew members and they ought to be transferable from one post to another.