You can edit that file directly or edit it via the Admin panels (Edit Titles)
Until the strangers hit the next plateau, they won't change unless you force the change, that goes through the database and rewrites titles to them. As to your Newly Registered starting to show, they probably had registered, and didn't post for a bit after they first signed on. The change happens as soon as the file is modified, just your observations of the change could've been delayed by coincidental occurrences.