in the original game I had fun progressing through home cities and choosing cards during level up, now we just improve the aesthetics of the home city, though some are funny “This is my pet rat plaguie”. Some civilations can’t customise the home city at all.
I think there are plenty of replacment flags that would be historically relevant. And have a (visual) effect in game.
For example the Germans could have the Prussian flag and the British could have the blue ensign (the predecessor of the New Zealand, Australian, and Fiji Flags).