forum.freeciv.org

I propose to create a function of Special administrative regions that allow to institute a different political system from the rest of the country in a single city like Hong Kong that have a political system different from China and Lenin's NEP.
I need to change my political system to communism because of a city that was constantly going in disorder (and temples, marketplace, courthouse, and women's suffrage was not enough), it would be nice to make this city communism and let the rest of the country be a democracy instead of change the whole country.

Hehe you cunning one Either you have rebellous city or lose trade bonus
Actually, you may just put a governor into the city or set a few citizens as entertainers manually.
But really, per-city control is bad here. Sometimes we would prefer handing some money to the citizens of few most troubled regions to make them more enthusiastic to work (like Soviet Union actually did) than change taxes or government for the whole country or let them hang out in cabarets.
Also, Civilization V has "puppet states" that much work like you described but have automated economy, and are a limited resource; setting governments per city for free would likely ruin the all gaming of finding the best ballance between advantages and disadvantages of each one.