We have two domains in our O365 tenancy: ourcompany.org and ourcompany.onmicrosoft.org with ourcompany.org currently being the default domain and on-prem AD synced to O365 using AD Connect.

I understand that Okta can't/won't federate onmicrosoft.org domain nor default domain. So in order for us to be able to add Office365 to Okta and make it work, we would have to make ourcompany.onmicrosoft.org the default domain. My question (to those who have similar setup and have actually done it in your environment) is did you run into any issues with existing users after changing the default domain to onmicrosoft.com/org? Please note that we're not making any changes to the UPN nor the email address in existing user accounts (their UPN/email address is still like this: user@ourcompany.org). Thanks.