Let's assume I change his leveling scheme to Black Necromancy and Summoning. Will he actually start to use summoning spells? On a similar note: If I were to change - let's say Virgil - so that he learns gunsmithy. Will he automatically get the dialogue option "What things can you make for me?" as the other followers who can build stuff?
Yes, Geoffrey should start using summons. It's general AI behavior. As for Virgil, no, that dialog option has to be manually added. P.S. You can use the Follower Editor to edit your followers' stats in-game.
Awesome! Thanks. Btw. if you really are Drog's Alt - meaning that you are the person responsible for the UAP and the High Resolution Patch (and so on) - everlasting respect and gratitude! Seriously.