Grey Guild wizard tweak balance question

[Avigor]

I'm looking at Sterling Vermin's Wizard of the Grey Guild and thinking to myself that I'm not a fan of the 10th level ability. Proficiency in 2 skills might be useful in some cases, but the main build idea I have for the class is a Rogue 3 (Arcane Trickster) / Wizard 17 (Grey Guild) with that feat that allows you to create ciphers and codes as the variant human feat and the Charlatan background who, while possessing the multiple holy symbols personality trait, secretly favors Vecna (not the strongest character ever, but I suspect very fun to play, and won't need the skills).

My proposal? Replace Practiced Conspirator with:
Enigmatic Schemer
Starting at 10th level, you and any magical items you are attuned to cannot be divined as if benefiting from the spell nondetection on an ongoing, permanent basis. This cannot be dispelled.

My question is: What does everyone else think about this? Is this proposed modification balanced or broken?