How to do it?

Yes, I found all of that you described above, but it's NOT the same. I really did make changes to turn centaurs into elves; there weren't any Sylvan centaurs or an experience system. My friend (we don't talk anymore; it's been about 10-12 years) did the game settings. Moreover, there was a feature where, in any castle and for any race, you could, for example, upgrade centaurs into dragons (but it was too expensive and took too long to play). We played on his computer, and I was 13-14 years old, and I didn't have a computer at home. So, I decided to remember this game. The game is great as it is; you can play an XL map with bots for a week, but I want that function where you can transform lower creatures into higher ones.