Adding Additional Fields in Decision Table of BRF+ Application for OPD

I am working on a requirement where the decision table DT_OUTPUT_TYPE of standard BRF+ application for output type determination OPD_V3_BILLING_DOCUMENT is required to be enhanced with an additional field. I observed to achieve it we need to enhance the structure S_APPL_PARAMETER which points to DDIC type - CSDBILDOCOMPRM. This basically directs to a consumption type of CDS view - C_BILLINGDOCUMENTOMPARAMDET. Enhanced the view by extending that with a new view. My view looks like below -

After the extension the structure is looking like below -

This allowed me to select the additional field PAYERPARTY in the decision table.

However, I want to know 2 things -

1.
a. Is this the only process?

b. What if I need to do some further calculation on the field(s) that I selected through the extension view before matching that with my entry in decision table? Is there an exit before the ms_vbrk moves to cr_cds_param in GET_TRANSIENT_DATA_BRF method of helper class CL_FDP_V3_BD_TRANS_DATA_HELPER?

2.
a. The view that I created to extend the consumption view should be of what VDM type? Consumption type?
b. Can this be annotated with VDM.viewExtension : true for further extension?

I'm new to S/4 Output determination technical side. Please advise.