For privacy reasons it is good for a gambler to change usernames with few emails. But if the gambler changes email address as the way he is changing usernames, it might affect him later either in the time of updating the KYC or documentation so email address should be sensitively handle. Many people don't know this so they use one username for all the casinos they are registering which will definitely complied to reveal your identity one day in the Internet. Though people are using one username for all for easy access.
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.
If you are talking about this approach on different casinos, it is possible and it is good for your privacy.
Emails can be different and evey throw-away emails if you are registering accounts for exploration new platforms and don't plan to use it for long time and with big fund.