Hello Prajakta,
Instead of adding a Z field in BRF+, you can have a Decision table directly mapped between Business Partners (of the Reporters) and the Support /Service Team. All the BPs having user id under a User group would be mapped to a particular Service team. The BRF+ rules and the relevant PPF action would determine the Service team based on the Reporter user group.
The Only disadvantage with this approach is - Updating the BRF+ decision table with new entries every time new Reporter users/ user ids are created.
Regards,
Kathir