[ovi256]

It must be, but publishing old passwords can still be done by saving the old cleartext password on password change.

[BeFlatXIII]

As in store "old password" as cleartext on its final use?

[macintux]

Yes, that was my initial thought on how to make this possible. In my case, the company where I contract has a dedicated application (on Mac, at least) for password changes: record the old password and share it once the new password has taken effect.