Wow... Eureka! I've got an idea!
I'm not sure if we can edit Shogun saves, but we can edit scenario starts in Medieval - in absolute free manner!

It would be quite simple thing - Game Master edit Scenario addind year in each iteration, starts game for each faction and send saves (not scenario raw-sheets) of each Faction to Faction leaders. Then Faction leaders send him their moves - make fightings in MP room on chosen charts with their Campaign armies and send results to Game Master.
He changes scenario sheets according to all player simultaneous moves, do all randomization tasks (including - Vices and Virtues appointing to some personages these guys become to be Famous Leaders in special field in scenario list) thenj - nest year starts.

Well, what do you think about it?

I will copy this idea into Medieval part of MP Campaign Forum, then if we will not find method to edit Shogun savesw - it seems like we can convert this thing into full-scale MP Medieval experience.