NCF – Extended list of Neutral creatures.

That's what I was thinking, whether it's possible to add them through the .exe file.

In theory, it's possible... but you need to be a GURU in reverse engineering, because without the source code, it's very difficult to add additional functions!

As an example, if you find the closed and open beta versions of Heroes of Might and Magic V (not to be confused with the alpha), you'll see that all skills and perks were defined by explicitly referencing the .xdb file – for example, now the spell "Plague" is essentially defined through a pseudonym like "SPELL_PLAGUE," but before, it was something like "\GameMechanics\spell_plague.xdb."

I'm saying all this because if you find a reverse engineering guru or learn it yourself, there's a chance to find the original addresses of the functions and then find them in version 3.1. Then, you can add an additional library to the .exe file; I forgot what it's called!