Doug's Musical Ability, in GURPS

[Mark Skarr]

I'm not familiar with GURPS, but could you 'buy' a limitation to prevent general spellcasting?

Technically, no.  It's a Skill, and that's all that the base-magic system uses for Spells, along with the Magery advantage (which Doug already has) which is where you'd tack limitaitons.  You don't normally see limitations put on Skills.  And the first sentence of Thamatology the skill tells you what it is:

GURPS, Characters[/i], pg 225]This is the academic study of magical theory and the “physics” of mana.

And it, basically, is what Doug wants.  I think.  He still might need Thamatology! depending on how Bob says magic works on the walk, but I'm not going anywhere, so I can wait for an answer.