You’re right that I couldn’t think of any explicit retcons. The closest I could think of, other than technology, were Burnham being related to Spock (which you touched on), and how absolutely decimated the Federation was by the Klingons while Discovery was in the mirror universe (again, not necessarily a retcon, but it seems like it would have been mentioned more).
Regarding tech, I had legitimately forgotten that Burnham’s parents and the time suit were Section 31. That said, what other amazing tech do we ever see out of Section 31? Granted, we don’t even see much of Section 31 in other shows, outside of DS9 and ENT, but in those cases, I seem to recall them being more intelligence operatives. They accomplish their job by knowing more than others, and operating outside usual Federation conventions. It’s spy stuff, not super weapons (outside the Changeling virus). But maybe I’m forgetting things.