Any user here would have a forum username that is different from their Apple ID, as publicly sharing an email address (or any personal information) would be unwise. The link between Apple ID and username is (shielded) somewhere on Apple’s servers. Usernames can have spaces, unlike email addresses. New or changed usernames will have to be checked for uniqueness.
When signing up for this forum, you would get a suggested username, with the option to create anything else for it. After initial setup, only the Hosts of this forum (Apple staff) can change it.
If you would like a different username (and not an email address), then you may request that.
Not sure if this works for Level 1 users (historically a Level 2+ perk), but …
- Try clicking the Report button on the right, for one of your own posts. Then message the Hosts staff about your issue from the pop-up message box. Select Username or Profile Issue as the reason.
Else one of the higher level users can relay this request for you, if needed. Then they would reply by email.