I believe that when a friendly empire (same family) takes over a planet from another friendly empire (still same family) that they should not act like genocidal bastards and murder 99% of the population. Instead, the leadership structure simply gets replaced by the new owners and the population continues to exist!
You’d have to also change some income formula stuff to make pop bankers worse because there would not be a single CF banker left in the game if this change happened! Research building pop bankers and preserving pop is a combo that would be absolutely insane.