Changing User Name

I'm looking for a way to change the User Name (login ID) of an existing
user w/o goofing up their password.

chuser allows me to do a whole bunch of stuff but not their name. Tried
Search-n-Replace on all key files (/etc/passwd, /etc/security/user,
/etc/security/limits, etc.) but the password gets broken (as I would
expect).

No rush if anyone has any ideas.

Thanks - Steve

AIX 5.X