Change Identifier Claim after the Authentication Provider is defined

Hi all. We have a Sharepoint 2013 working ok using claims based authentication, ADFS and a third-party Identity Provider. However, "somebody" has decided to change the Identifier Claim from Email (the current one) to some other attibute (driving license ID, let's say). I assume there are implications with this change (mainly that existing users will be identified as new users as their identifier changes). We can assume this, however, I cannot find how to change the identifierclaim property within the authentication provider. Is it feasible to do that change?

Any help will be appreciated

Thanks in advance

// Raúl - I love this game