Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Hello Mike,
I am glad to help you here.
Here are the answers for your concerns above.
- Yes, if you want to rebrand in Microsoft 365, as far as I know you just need to change your Microsoft 365 tenant name ( for example currently is Contoso, and you could change to other names as you wanted). Please note, the tenant name changes may take some hours to be reflected through your whole Microsoft 365, thanks. For your reference Change your organization's address, technical contact, and more.
- Yes, you don't need to purchase a new Microsoft 365 tenant, if you need change the user's UserPrincipal Name, SMTP address etc, you just need to add and verify your new AD domain to the current Microsoft 365 tenant, after that change the user's UPN, SMTP etc from local AD, then re-sync them to the current tenant. For your reference Add a domain to Microsoft 365.
- for the SharePoint Online URLs and OneDrive URLs in Microsoft 365, as far as I know the onedrive url would be also changed after the user's UPN was changed. For your reference https://docs.microsoft.com/en-us/onedrive/upn-changes. However, for the SharePoint Online URLs, currently we could change few parameters in the url, and it is not supported to change the old domain included in the SharePoint URLs. For more details, please refer to Change a site address.
On another hand, as this thread is related to Microsoft 365 Azure AD, Exchange Online and SharePoint Online, if you have concerns about the third option of SharePoint Online/OneDrive, it is recommended please post a new thread in this forum under Microsoft 365 for Admins/SharePoint Online/Microsoft 365 for Business category, the dedicated support engineers there are mainly focusing on SharePoint/OneDrive related, thanks for your understanding.
Please feel free to share with me if you need any other help, thanks.
Best Regards,
Oliver