There's a simple solution to this problem: Role-based authentication. PhpBB3 implements this through the group system. I could, for instance, create a group called "Duke of Brookshire", give all the relevant user and moderator permissions to it, and put in the current duke as its only member. Then if the duke were to change I could just remove one member and add one member in the group instead of going through two different sorts of permissions on a whole bunch of forums.
The problem? If I did that, the moderators of Brookshire would just be listed as "Duke of Brookshire". You could find out the duke by clicking on it (it would be a link leading to a list of the members of that group), but I know *I* like to be able to look at the forum and tell who's in charge of what at a glance, and I've heard a lot of other people also do.
That's why I actually did something useful today and modded the board to display, in forum moderator lists, the members of groups along with groups themselves. The one place where you can see this at the time I'm posting this is the Landsraad, where the current voting nobility is listed in the moderators list. Don't ask me why all the voting nobility are moderators - they certainly don't need to be; it just was that way when I took over board administration and I haven't bothered to change it :P.
I'll be rebasing most of the relevant roles todayish - the kaiser, non-ruling steward, praetor, arbiter, the ministers, the dukes, and the barons spring to mind. I'll probably not roleify counts, though, seems too much initial trouble to me for such a small long-term payoff... but we'll see.