Allow permiting allies mid-game

Is there any reason why the allow allying option cannot be changed in the middle of the game? It's silly not to be able to change it mid game

Sure, you are admin, you ally another person, then you turn it off to prevent other players from allying. They cannot send money to each other, can't safely attack the same cities, etc...so you and your ally have a leg up

Turning the option off should break all alliances, but I guess I can see how it could be a problem. It just seems like the admin should be able to change it

I think this a long death topic, but i think there should be a gamemode in where you can,t ally during the first 15 turns, and then you can ally.