Create Site for any Domain owned
You are limited to the first domain name registered for all sites. https://support.office.com/en-us/article/Can-t-rename-team-site-on-Office-365-576325ad-8c40-4fe8-8a63-68c3b7d536cf?ui=en-US&rs=en-US&ad=US
You should be able to create a new site or migrate the domain name to a new name without having to delete your entire Exchange and SharePoint data and creating anew account
Eduardo Valverde commented
I can't believe on it. You should tell it before we create a new consumer tenant.
This single issue continues to cause the Office 365 house of cars to fall. It's so inconvenient, that we don't promote the use of Sharepoint within our company. Not until it makes scense for people who don't even know what Sharepoint is, or what to do with it. And that's a real shame, because Sharepoint as a platform is pretty amazing, but Sharepoint Online is broken from a URL/unique domain name sense. We all share the same base domain name of *.sharepoint.com, which is quite terrible when you think about it, and what we could do if we could truly individualized deployment of our Sharepoint sites & URL's to "sub.domain.toplevel" which just makes sense to most people, even if they don't understand why. accounting.consoso.com is far more expensive than accounting.contoso.sharepoint.com. or even accounting.sharepoint.contoso.com would work, should base DN be needed elsewhere in the online presents. A shared URL across all tenants just stinks, nevermind the fact that it affects what we can do with Intranet and Internet zone access rules and BWM policies in our network equipment and edge firewalls. And masking everything via DNS records is not really what DNS is for, and it's labor intensive to maintain for even a mid-sized (500 employees) tenant. Trust me.