There were never any Rules preventing any Staff from being HA in more than one League. The final decision on selecting and appointing any HA rests in the hands of the President.
In the contrary we always had many HA positions filled by the same person, especially for new and struggling leagues.
All corporate staff may be HAs in any League; and specifically the Leagues Directors are supposed to be HA in all leagues not having an active HA. This policy was reaffirmed by having PSTDs appointed as HAs in several Leagues.