Changing UPN of O365 federated Users

Every user synchronized from on-prem Active Directory onto office 365 must use their UPN (UserPrincipalName) to login to any of the O365 services. However if an organization having a very old operational Active Directory probably be using NETBIOS (domain\user) way of login to on premise workstations/applications. To overcome this, administrators enforces the UPN as the …