How to do it?

Creating Sylvan Centaurs.
Script 00, option 009, Author: Slava Salnikov
This option allows Rampart heroes to create Sylvan Centaurs for free by combining High Elves and Centaur Captains.
A Sylvan Centaur has the following parameters: attack 10, defense 5, damage 4-6, health 15, speed 8, attack 24, Double Shot.
To create Sylvan Centaurs, hold down Ctrl and click on any unit of High Elves or Centaur Captains. The creatures will combine in a 1:1 ratio, i.e., if you have, for example, 42 Centaur Captains and 14 High Elves, you will end up with 14 Sylvan Centaurs and 28 Centaur Captains.
If option 900 "Creature Experience System" is active, Sylvan Centaurs will lose all the experience accumulated by the High Elves and Centaur Captains, but after that, they will gain experience as usual.
Creature Experience System.
Script 00, option 900, Author: Slava Salnikov
A global option that fundamentally changes the hero leveling system, the use of creatures, and their tactical advantages.
With option 900 active, creatures led by a hero will gain experience after each battle and can increase in rank, developing their parameters and/or abilities. Bonuses will only be visible in battle and may vary for each type of creature. Creatures without a hero do not gain experience...
The current rank (if > 0) is displayed as yellow birds (the ^ symbol) on the full image of the creature above the numbers
indicating the unit size. Five birds are replaced by an image of a sword. The maximum 10th rank is 2 swords...