How to change the unique identifier in CP/Console (replacing the email)

Content

Hi,

Our client has many customers that don't have email, so it is not possible to keep this as the unique identifier.

Client wants to make the "National ID number" ("DNI" in Peru) as the (custom) unique field identifier. Customer only have to enter his DNI and work with that identifier, without email.

How could be the best way to do this?

 

Looking forward your comments,
Thanks
David

Version

November 2014