Is it possible to change the field used to identify contacts in the search bar?

Hello,

When submitting an SR, I understand that it is possible to register a contact without an email address.

https://docs.oracle.com/en/cloud/saas/marketing/eloqua-user/Help/ContactsWithoutEmailAddress/ContactsWithoutEmailAddress.htm

In this case, since the email address is no longer the primary key, is it possible to change the field used to identify contacts in the search bar?

For example, using Contact ID or a newly created custom field.

Regards,

Jinjoo