Here's a screenshot of one of our current Azure subscriptions:
Is it possible to rename the domain for .. say Pew pew #1 from someLameLoginUserAccount.onmicrosoft.com to purekrome-pewpew1.onmicrosoft.com
(assumption: that FQDN isn't 'taken' on .. I guess Azure AD).
Shui shengbao
No, it is not possible. Please refer to this answer.
Is it possible to add a new custom AD and then drop/delete this ***.onmicrosoft.com AD? NOTE: this is before any resource is created/add.
No, it is also impossible, you could create custom AD, but you could not delete the default Azure AD directory(***.onmicrosoft.com).
来源：https://stackoverflow.com/questions/44103418/is-it-possible-to-rename-an-azure-subscription-name-domain