Hi Nitesh
From the description of the note, it looks like that new consumer job only allows body content customization. Unfortunately, looks like email subject cannot be customized.
If you really need that you might need to build your own custom alerting mechanism. One such approach is to build a custom alert consumer job and access the alerts via the alerting API. More details in the links below.
Michal's PI tips: Component based message alerting - API
Alert Consumption - Administering Process Integration (PI) - SAP Library
Rgds
Eng Swee