While I find it amazing that you can remake the Central Powers, wouldn't it be better if you could do this without having to go unhistorical and pray the that RNG god favors you?
The rejoin the Central Powers focus could add decisions to start a monarchist revolution in Germany, which depends on their non-aligned popularity.
If you manage to get Germany at least 40% non-aligned with spies, you could start a civil war with that focus. Or if it's already non-aligned, the Kaiser simply returns.
To start the Rejoin the Central Powers focus, Germany must not be at war and have at least 40% non-aligned popularity.
The Turkish AI won't use spies that way, so only a Turkish player can do that. While a German player can easily counter the Turkish spies with fascist demagogue and/or their own spies.