I wouldn't think he even needs a personal tragedy. He already recommended surrendering to save billions of lives. He already kidnapped Sloane and invaded his brain. He already started to entertain the notion that his intelligence made the rules apply to him less. He doesn't need some contrived personal tragedy to reach "The ends justify the means when lives are at stake", it's the logical trajectory of his development. He can empathize with the loss of innocent life regardless of whether that life is the one he is in love with.
Just, I don't think he'd ever cross the line of killing for Federation political control, he's only apply it to cases of mass casualties.
I'm not a fan of that trope that somebody can be okay with millions of strangers dying, but the one person they have sex with dying, THAT crosses the line.
Recommending that the U.F.P. surrender is not breaking any rules; he in fact stopped the other augments in that episode who were willing to break the rules to realize it.
I agree that he broke the rules to get the cure from Sloan, but the
D.S.9. crew, Julian included, did such things on many occasions before — bending and slightly breaking the rules is quite a bit different from being a member of an illegal secret police that makes suspected enemies of the U.F.P. disappear
sans due process, nor accountability of their own actions. Remember that in
D.S.9. Section 31 was very different from how it was later portrayed in
Discovery, where it was merely a black operations intelligence organization that nevertheless had rules, a chain of command, and answerability to civilian leaders — In
D.S.9., it was an illegal, unaccountable, officially nonexistent secret police, that most of
Starfleet did not even know the existence of.
In
Inter Arma Silent Leges,
S. 31 framed an innocent man to potential execution to get their mole, something Julian protested passionately and would never agree to in his current state. I envision a Julian to whom many things happened that would make him jaded enough to view the sacrifice of one innocent man acceptable for the common good.