how to create changing flags in civ IV

[AstrokauzazITS994]

CHi, I'm thinking about creating a mod about the history from 1910 to 2023. I thought to myself, but then flags changed as well as leaders and names of countries. Germany will be an example.In the early 1910s there was Prussia which had two black lines at the bottom and top and a coat of arms on the flag. Later on the top of the flag was black. white in the middle. And red at the bottom. The next flag of Germany was a typical German flag except that there was a cross in the middle. After that, the flag of Germany had a red background with a white circle in the middle with the symbol of Nazism. Later, there was a division of Germany into two parts where federal and democratic Germany changed the flags. In 1990, federal and democratic Germany merged and also changed its name.
I would like the flag to change in a specific year and month or in a specific era. Does anyone know a script that allows this?