Nameless Hero
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RTA has a different approach – it's all about the map, and you can add scripts to the map. I browsed their website and found that they also have a different executable file (for map version 1.21.2.1+).
Many interesting features are implemented using scripts; the executable file probably expands the capabilities of the scripts. For example, NHF also switched to a new engine because of the unlocking of combat scripts.
Using the script editor, I delved into the map files. I only found mentions of "chilling_steel" as a skill. However, it doesn't seem possible to change its values. There's no doubt that mastering the art of writing "workarounds" or scripts is necessary here.