Disable Change Password
User Configuration\Administrative Templates\System\Logon/Logoff
Prevents users from changing their Windows password on demand.
This policy disables the Change Password button on the Windows Security dialog box (which appears when you press CTRL+ALT+DEL).
However, users are still able to change their password when prompted by the system. The system prompts users for a new password when an administrator requires a new password or their password is expiring.