[Thaumatology] A very different take on the Demonologist

[Anaraxes]

Seems like fine background color.

adding or removing one Trait or Meta-Trait, and then adding or removing another, and paying any point difference if necessary

So, the demonic contract is just backstory for why the character is the way it was built. Demonology apparently isn't a particular body of knowledge, or a skill/advantage in and of itself. It's a reason in the setting for allowing exotic and supernatural traits to be possessed by PCs.