Pranav,
you have 2 requirements:
1 - Profit Center
2 - Material / Quantity
1 -
According you scenario the Profit Center is assigned in P&L line item. How could you have it in FBL1N since it only concerns vendor line items? You can do that by User Exit or BTE.
2 - Material/Quantity was disabled in FBL1N since funcionality activation of multiple P.O per single Invoice. In this case you can have one Vendor Invoice related several materials master. What you can do is a development in order to check P.O and Invoice to fill Material field in anothe FBL1N field regarding defined criteria.
Best Regards