Sorry, i don't know what trac is, and i'm afraid i don't have time to investigate properly....
Can't you just set all the users to need to change their passwords when they next log in? Hmm, looks like you can only really do that if you reset their password at the same time... and so would need to share that new password with them... this happens in
Can you not just get them to reset their passwords (via a link to their email)? I guess not
The only other thing i can think of is you add some code (locally) in
\UsersLib::validate_user_tiki when their password fails, to check if their password matches using MD5, and then trigger the "must change password" code if so...
Tricky one! HTH