Out of curiosity, any one ever tried to load a world state with all mages killed in circle of Ferenden as Cullen requested?
I wonder if that changes his dialogue in DAI. Is that too evil...
"Evil" aside...
I've imported world states with the Ferelden Circle both annuled and saved, and Cullen had no different lines whatsoever, or even any reference to the annulment in his rants about the Order. He did have a different line in DA2, but in Inquisition neither decision gives him any unique dialogue.
If you're wondering this because of the Keep tile about agreeing with Cullen's request to annul the Circle, that tile was added way too late in development to affect anything, it showed on the Keep only about a month before launch. It's just a flavor tile that doesn't really trigger anything in-game.