This is what I do: typos and small mistakes, I correct,
without annotation. Same for additional text, but only
very shortly after submission.
in reply to Post-Posting Etiquette
Any larger changes I post as a reply to my own post - and
never with a bold update. Why? Because a reply will go into
the newest nodes list, while an update doesn't. If you
update a post I already read, I probably never will see your
update. But if you reply, I will at least be made aware of
it, and if the thread interests me, I'll read it.