Users with MFA, Change autentication

My experience is that the configured MFA methods are not directly impacted on the backend. However, I've not recently tested what this does to eg. the Authenticator App if that's being used as one of the MFA authentication methods. I would recommend to test this change with a single user on a test account to determine exact impact. Microsoft has a page that describes the impact of UPN changes in Azure AD available at https://docs.microsoft.com/en-us/azure/active-directory/hybrid/howto-troubleshoot-upn-changes