user xyz recently married.  If I understand correctly, I edit her email address, create alias with married name, set married name alias as primary which will make original name secondary.  All mail whether old name or married name will arrive in the one mailbox.  I edit Display Name to married name.
When creating new email, replying, or forwarding it will show from married name and married name email address.
I reconfigure outlook to login as new married name email address.
EXAMPLE  - current email address xzy@abc.com, add alias xyzmarried@abc.com, make xyzmarried@abc.com primary, configure outlook to logon using xyzmarried@abc.com
She wants to keep old and new email addresses indefinitely and not have to pay for an additional license