Cannot Update Office 365 Default Email Address Policy for Distribution Groups

Hi,

We are running a hybrid of Exchange 2013 and Office 365.

We have just added a new domain to our emails, I did this on our local Exchange Server, and then ran the hybrid config tool to push the new domain over to office 365, also added the domain to office 365 and verified it.

Emails are flowing fine on the new domain, and users have the domain as an email address.

Local Distribution groups also have the new domain attached, and are working.

But... the distribution groups that exist only in Office 365, do not have the new domain attached.
If I went to create a new group there is an option to create with the new domain..

But, I cannot figure out how to add the new domain to the exisiting groups.

I have run this command on an Office 365 connected powershell:

Set-EmailAddressPolicy -identity "Default Policy" -EnabledEmailAddressTemplates "smtp:..."

But it just returns: You are not authorized to perform this operation on e-mail address policy "Default Policy"

and I am connecting using Office 365 Global Administrator account.

Does anyone have any ideas how to add the new domain to the exisiting groups, without manually updating all the groups.

Thanks,

Tim Jeens