Does this mod modify and RPK files?

@Rime The mod is made by editing the HumanoidRig.clb directly and so what people are effectively doing when they install the mod is they're overwriting the entire file. you can find it in \SteamLibrary\steamapps\common\Age of Wonders 4\Content\Title\Libraries\Figure_Rig

if you don't see your changes you might have save as the file to a new place then, place into that folder to overwrite it OR make it a mod and add it to your mod folder and run the game with it on. the mod's folder is located at

Documents\Paradox Interactive\Age of Wonders 4\Mods\