Because of the way it works, one can use Heroquest to run Communities as Player Characters without any specific rule changes. You just have to describe your community in terms of the abilities it will use to solve the problems the campaign will throw at it, and, in play, frame the contests, and describe the outcomes approriately for the communities you are playing. Because there are no "mandatory" abilities there is no "translation" as such (using d20 rules to run a community, you might struggle over how to stat up a city's DEX for example), You might want to think about what keywords are appropriate - even if every community has the same one, it can provide a useful "baseline" for some abilities (In a "regular" Gloranthan campaign, all the PC's may be "member of the xxx Clan". In a "Community" game where the players are running the gangs of New York during the Prohibition, each Player Community could have the "Criminal Gang" keyword etc).
A community might have individuals as the supporting cast members (Henchmen, followers etc) who can act or augment as appropriate (I think this is "sort of" how KoDP works where a clans ability can be augmented by the individual sent to lead a delegation when trading, negotiating or exploring).
The rules also provide for using communities to support individuals - The Clan questionnaire in S:KoH (and, I think on the website, but I can't check the address at the moment) creates a set of "Standard" communtiy resources, and some of the events in the Colymar campaign (again in S:KoH) show how these might be used