I have an application with hundred of users created using the built-in Salesforce Identity and Access system.

This appears to have been a mistake.  These users and user accounts could have been configured to use the Active Directory (ADFS) via Azure AD.  If I configure my Salesforce instance to use Azure AD (ADFS) at this URL, https://docs.microsoft.com/en-us/azure/active-directory/saas-apps/salesforce-sandbox-tutorial  will it BREAK all my users in my Salesforce application?

Is there any way to easily migrate all of the existing using with a SF identity to match the email address for these hundreds of users that already have a username and password in Active Directory without breaking anything?