I cannot test it locally due to my OS security policies, but the following may work:
1/ just in case - create a copy of [email protected] operator (save as),
2/ open Security Polices and:
- check "Enable frequently required policies"
- set "Maximum operator password age in days" and "Minimum operator password age in days" to "1"

3/ logout
4/ Shutdown the server (shutdown.bat)
5/ Change date in the system one day ahead.
6/ login as [email protected] - you should be forced to change the password
7/ Reset Security Policy appropriately (or disable).