Hi,
I'm not FlexRay expert but the module on MPC5748G is designed according to FlexRay 2.1 Protocol Specification. This one talks only about pKeySlotId.
pSecondKeySlotID is specified in FlexRay 3.0.1 Protocol Specification.
So, the answer should be that this is not supported by MPC5748G.
Hope this helps.
Regards,
Lukas