RTF is a global modification that replaces all towns in the game.

I have an idea! Would it be possible to implement an improvement system for creatures in a human training hall, not within the castle, but by upgrading each tier to a stronger creature of the same tier (e.g., slightly increasing stats, adding +1 ability, and slightly recoloring the textures)? The number of improved creatures would be equal to (skill level) * (hero level) + (bonuses from individual skills).

Added 1 minute ago
I was just digging through the game files and saw the upgrade system, which is where this idea came from.