Pixelfed does have a command to reclaim usernames that conflict with our list of ReservedUsernames, and I've had to use it a few times.
I don't anticipate any future uses since our web/api routes are nailed down and this is the only reason we implemented this.
https://github.com/pixelfed/pixelfed/blob/dev/app/Console/Commands/FixUsernames.php#L74-L79