What happens when downloading new leaders for existing civs?

Maybe this is a stupid question, but if I download a new leader for an existing civ, what happens? For example, there is a mod for Germany that has Frederick as its leader. Since it's set up as an entire civ, does that mean that a game could have two seperate Germany civilizations each competing with each other? I'm kind of betting this is what happens, just wanting confirmation.

Thanks!

JHaganOSU

That depends on the mod. Quite a few older ones do replace existing Civs.

Most mods from JFD, More Civs, Colonialist Legacies, Patria Grande, RawSasquatch and others on the first couple pages of the New Civs forum generally don't. In the case of JFD's Civs, you could end up with 5 Russias in a game - Catherine, Peter, Nicholas II, Lenin's USSR and Stalin's USSR (and he plans on at least two more Russian leaders). He does, however, have a Roman leader, Julius Caesar, that replaces Augustus, but he explicitly says so for that mod. Some leaders edit the original UAs and other unique components of original civs as well, so make sure you read the description before you download!

tl;dr: Most recent civs don't replace, they just add. But make sure to check its description to be sure!

Someday I'm going to have to remember to start a game with all JFD's Russia's enabled and then turn on Autoplay with Live Tuner, just to see the 'funs'.