Hi Murli,
You can try below option.
Create two different pricing procedure (one with additional pricing condition) and do determination of pricing procedure in billing document based on that billing document type (Bill Doc. Pric. Proc, Cust. Pric. Proc. and Sales Area).
For Proforma Invoice, you can determine pricing procedure with an additional condition type.
You have to maintain copy control according to your requirement.
Thanks,
Pratik