Modding

the items that appear in the town – in the file MapObjects/town_name.(AdvMapTownShared), change the lines MagicSchool_0 and MagicSchool_1 (at the very end of the file). If it's specifically for a hero class, you can change the chances of skill drops, including magic skills, for any faction in GameMechanics/RefTables/HeroClass.