What would you like to change in Heroes of Might and Magic III?

Khota is not an add-on, but a fan-made global mod. And I don't remember them doing such things there; maybe the idea was there from the beginning. There's something similar in Woge: in some factions, at certain levels, there are two types of creatures, and you can choose which one to build, but this only adds to Woge's unnecessary complexity, of which there is already plenty.

Yes, of course, it's a mod, not an add-on.
But they planned to do it (see the discussion on the initial pages and specifically about the Bastion city); I don't know if they did.
In Woge, there isn't a function to choose which building to construct as such; you need to enable the corresponding setting, which allows you to change creatures somewhere (e.g., Rust instead of Phoenixes, Fairy instead of Golden...).
However, Woge does contain too much new content, which "overloads" it. New features are good, but only in moderation. Fortunately, they can be disabled.