I mean, first of all, that’s exactly the kind of thing nobles did. I know the word as an adjective in current usage reflects the image that nobles want people to hold, rather than the reality of assassinations of both reputations and persons for political and personal ends, but I think that the distinction is material to the discussion.

Garak is conflicted about many things. He’s a brilliant and multidimensional character - a torturer with a heart of gold - and it is exactly that Janus-like relation to morality as conceived of by Starfleet that makes him so key in the Dominion War. Like Division 31, his character brought into relief the existential question of the role of intelligence services and dirty deeds in a liberal democracy. The Roddenberryverse Federation was the Galahad (or at least the Lancelot) of the galaxy, and the occasional dark aspects that surfaced invoke the role of organizations like the CIA in a democracy. Garak, as a Cardassian and officer in the Obsidian Order, adheres to a broadly different morality, but ends up aligning with the Federation because of his conscience. His multi-faceted relationship with Bashir is often used to show his “odi et amo” relationship to the Federation.

In any case, I think that I’d have to characterize Garak as “noble.” He was constantly thinking about the big picture and the greater good, even if the deck he was playing had a few more cards than some of the Federation folk were comfortable with. If you define “noble” as being completely exclusive of “evil,” then the character concept of the OP cannot exist. That would be a shame, because it’s an interesting concept to explore.