We are working on providing the ability to change the email address (both primary and secondary) associated with a group.
Roadmap item: https://products.office.com/en-US/business/office-365-roadmap?filters=&freeformsearch=27891&featureid=27891Jens Spaniel supported this idea ·Jens Spaniel commented
I checked the linked roadmap item. This does not meet the requirement. The roadmap item is about a powershell cmdlet. But the requirement is adding email aliases to an Office 365 group via the portal - as this is supported for DistLists and users.
Adding an alias already works with a powershell cmdlet, but most of the users like to see this in the portal.