Perhaps I misunderstand the way this game is supposed to work. I thought the point was that, while we should take actions that are realistic for our nations, we can also attempt to change the way history went. This would involve changing directly the personalities of the leaders of our nations. That should be allowable.
IF we go too crazy, then the GM can simply say that something failed or we met with rebellion.
As far as power goes, those who have power have it because others let them have power, or assume they have it. If the Emperor can convince his people he has power, then he will have power. Simple as that. A military coup, to replace the Tokugawa Shogunate, goes a long way towards helping that.
I know y'all have played this before, and made the game, but is there really a problem with each new playing shaping and changing the way things are done and perceived? I'd think it would be boring if it was always the same.