No. Discourse does not allow spaces or (most) special characters in usernames. That’s why they got re-written.
I don’t understand what you’re saying about URL.
It has to use something to generate a username.
It does this:
UserNameSuggester.suggest(
opts[:username].presence || opts[:name].presence || opts[:email],
So if you don’t have a username or a name it falls back to using the first part of the email address.