Renaming of O365 groups

Ivo Essenberg You can add a proxy address to the Unified Group /Office 365 Group and then set the new email address as the primary email address. This will change the email address associated with the group. This might not modify the URL of SPO although. 

1. For this connect to EXO PowerShell and run the below command to add required SMTP as an alias. 
2. Set-UnifiedGroup -Identity "abc@contoso.com" -EmailAddresses: @{Add ="xyz@contoso.com"} where abc@contoso.com is the email address of the Office 365 group and xyz@contoso.com is the required Email ID.
3. Promote alias as a primary SMTP address, Set-UnifiedGroup -Identity "Test O365Group" -PrimarySmtpAddress "xyz@contoso.com"
4. If not required, you can remove the first ID using below command.  Set-UnifiedGroup -Identity "xyz@contoso.com" -EmailAddresses: @{Remove="abc@contoso.com"}

Please note, For updating the Office 365 group SMTP address required Global Administrator access.