its a specific wargoal called great war capitulation, but works much like cut down to size. I dont know the details about how the great wars mod work, but any disassembly of a country I think is already handled by the existing mechanics, eg the attackers can demand release of countries (AI in 2.3 is more interested in this) and during terrible wars nationalist rebels are not unlikely to pop up.
there are a ton of countries, imaginary and otherwise that could be added. We decided to add 3, but ended up with 5. Doing a united states of south america did come up, as well as a greater scandinavia, but truth is you could go on forever
I hope some mod adds them though