Search term exclusion: TIL! I swear I've tried that w/o luck before. Possibly was confounding that with OR pairing, usually given as "(termA|termB)". I'm pretty sure that doesn't work as expected (and just tested it). It's also annoyingly absent from DDG search, which is out of scope for here.
I'd been made aware of the undocumented endpoint but didn't want to spill the beans ;-) It's apparently expensive. OK to run manually, but don't script it.
Just guessed another two undocumented endpoints "deadcomments" and "deadstories", these take you to a special admin login page if you're logged out, or say "Unknown." if logged in:
/flagged, /upvoted, and /favorites, with an "?id=<your_userID>" are how your own flagged, upvoted, and favourited posts/comments are displayed. "&kind=comments" specifically returns flagged comments, otherwise posts. For upvotes and faves, the argument is "&comments=t", for consistency one presumes...
Favourites can be displayed for other users, upvoted and flagged cannot (for mere mortals).
I suspect downvotes can also be displayed, though I don't know that syntax.
The replies/by is particularly handy in sorting out why a dead account has been banned, or if there've been previous moderator interactions. That's my own principle use.
On the second point - HN has an undocumented endpoint https://news.ycombinator.com/replies?id=skeptrune&by=dredmor... but that doesn't give you search of course.