Use the ICISite interface SetPassPhrase method to change a private key pass phrase. If you must restart the server for the changes to take effect, the SetPassPhrase method returns a value of TRUE.
[in] BSTR newVal,
[out, retval] VARIANT_BOOL *pNeedRestart);
Refer to Site Certificates and Keys Parameters for an illustration of how this and other ICISite methods can be accessed in the Administrator interface.