JG2400

As I am asking in the title. The hypothetical nations would most likely be Italic in nature, and those three nations are closest without being Italy proper. I know San Marino is a popular choice, and Malta seems semi-popular. Monaco seems rather rare.

Maybe Qualification rules will help you out? Perhaps helpers as well. Austria has a system where they pick Qualifiers out of a mix of both the Upper and Lower group; might be able to reference that

Hello, I am considering the possibility of making a 1800s-inspired database for FM24. As the title says, I'd like to get a general idea of what nations are more/less flexible in terms of being overwritten with another one. Thank you!

I don't believe that is the case, because IIRC Russia's id is banned via hardcode. This FM23 mod, for example, had to transfer everything from Russia to the Soviet Union in order to put them back into UEFA Continentals: https://steamcommunity.com/sharedfiles/filedetails/?id=2886950813 Though it's not impossible that someone in the SI Russia wanted to double-ban Russia, or something. I don't believe it's the UCL changes either, because I don't think this problem existed in FM21 with the start of the ECL?