A better way to do this would have been:

* hash current passwords with a salt, unique to each password entry, and throw away the plaintext entries.

* keep a history of hashes per user, to prevent changing to a past password

* ensure fair complexity of the incoming password

* once the deadline has been reached, force users who have not yet changed their password to do a password reset via an online form

* never, ever again think that doubling a password is a proper way to fix a security issue, ever...