On Duelbits you can change your account username but I am unsure about it on other online casinos. Most online casinos don't allow users to change usernames and it's the same for account emails. If you are talking about changing usernames and email addresses on one casino, it's less likely possible.
I have not seen a casino allowing me to changed username. Though I have not tried checking duelbits to know if they changed username that has been accepted by them. And I know of the changing of email address in a casino after the registration but not username. And I mean using different usernames with different casinos for privacy purpose. With that people will not know that you are the owner of the other account in the other casinos. If someone has seen the username in casinos and other platforms.