1) Ah, it doesn't change in the settings... And what exactly did you change in Shared? The ID? Was there a dropdown list? And yes, in principle, with specific specializations, the settings may not display correctly. Although this is unlikely to apply to a Dark Sorcerer, ideally, field tests should be conducted.
3) Ugh... If I remember correctly. It seems to be a setting in MapPropertiesTree. ReservedHero(es). Plus a special script to summon the enemy.
4) It's definitely in the manual. There should be a file with the IDs.