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The nickname only appears if your uNet user database already contains the same username.
For example, if I have a user that's named "Admin" already registered at my site and another person registers through uNet on my site, that has the username "Admin", uNet will automatically append random characters at the end of the new registered member. It's suppose to make the naming conventions unique so you won't have search issues and/or overwriting previous users.
Long answer short. You can't.