I don't see any rules that would disallow it. It's a grey area, but one that would have to be fixed with a mechanical change rather than punishment for people using the optimal condition.

Now in the context of the game not sure on the BD's call of actually voting in favor of him, logically the sellsword upon becoming neutral king would be quite a liability as he then could just as easilly side with the NK or unseen/cult if it came down to the line (and actually could quite possibly be favorable, as they would be more likely to be able to kill him)

Slandering parties without any credible evidence is a sign of a troll.

Do not feed.