I've thought of a way for Salonica to keep its Jewish character, though I'm afraid you're not going to like itWe're drifting a bit off-topic but yeah...it's an interesting point you make nonetheless...
What made it really interesting was that it was already a layered established society within not only Salonica but Northern Greece in general. Though of course many of the local owners of businesses and industries were Jewish(edit: And don't forget that Salonica was till about the 60's way more industrialised than Athens/Attica had been the past 400 years.), there was a very populous middle-class Jewish community, and an even more populous lower-class one...Jewish people of all walks of life called this place home...and Ladino was a very useful language to be able to speak if you were visiting...
To be fair though, even after Salonica was annexed back in 1912, the Jewish community managed to maintain its influence over Salonican affairs till the Nazis "relocated" them in the 40's. Though it'd be lying to say they prospered they were at least not openly discriminated against. But I do know for a fact that there was a "Jewish" party in local elections and prominent local Jews were elected into the city council consistently, many of them receiving the majority of their votes from their Orthodox constituents.
I mean, and that is funny if you think about it, during the years prior to WW2, under Metaxas' regime, when a sort of Fascist Youth was established, there was consideration to allow Jews to join......somehow that didn't happen through...
Also another interesting point is that when the local proletariat had radicalized itself and local disgruntled industrial workers started actively voicing their demands towards the industrialists, among the most prominent figures on both sides of the fence were Jewish...the Jewish industrialists owned the flourishing textile industry and the Jewish industrial workers were the ones that despised them most for it...
All in all, I still hear all those stories from survivors and Salonica in the 40's strikes me as a much better place to live in than Salonica in 2012...
Bulgaria did not deport its own Jews during WWII, so if Salonica had been part of Bulgaria (a possibility that some of the Jews supported), they could have survived. Though they would probably still have immigrated to Israel, so that might not work either
Of course with all the butterflies involved, it's quite unlikely that the OTL circumstances would be repeated, so it's probably a silly idea...