This is not the function of the MSC, it is the function of the ME.
When the subscriber dials #31#SN, the ME will understand that he want to temporary invoke CLIR for a single call, and it will sent this request along with the nbr of the called party to the MSC in the call setup message.
The #31# is the standard prefix for temporary CLIR invocation, and the ME must intercept this prefix.
If you do know another SCI that must be declare in the MSC, plz let me know.
Regards