MOD: Armageddon's Blade

Well, to be honest, I don't know what I know. What's an "extra expert" to me is just commonplace. I learned about it in the old NHF, and it's included by default in the NOIADE character calculator...

I certainly know about the existence of the Extra level, but I'd like to clarify a few things.
1) Does the Mastery Amulet only work on the Hero's primary skill (i.e., in most cases, their faction skill), and does it not apply to other skills in a normal situation, thus having no effect? (I'm just clarifying the practical usefulness of the Artifact.)
2) So, you simply edited the necessary Spells for the Extra level and added the Creature to the Spellbook with the Extra level. Does that mean it's quite simple?
3) Some Creatures also have Mastery abilities. Since they are added to the Spellbook, can you change the effectiveness of some of these abilities in a similar way? (Have you tried that?)