The feature was not added in IWCS because of a possible performance issue in the OfficeScan server where it is attached to.

If there are more OfficeScan clients (>1000) that will be using Smart Scan, then it is not reasonable to enable the integrated SPN server because of performance perspective. In this scenario, you should set up a stand-alone SPN server and edit the approved/blocked list there.

On the other hand, if less clients (<1000) will be using Smart Scan, then enabling the Integrated WVS is enough. In this case, you can use the approved/blocked list in the OfficeScan Web Reputation Service configuration section, which can support the granularity to domain/client level.