you can use these two programs for basic modding of the game: https://github.com/AssetRipper/AssetRipper/releases https://github.com/dnSpy/dnSpy/releases
you use assetripper to extract the game's code into a readable state, then use dnspy to inject your edited code into the game
do note though that you'll have to learn the game's format for skills / unit setup first, you'll be able to see the format / entries with these files: Class.cs, ClassList.cs, Skill.cs, SkillList.cs