There is already a field right of account number, company code (here hidden, intended for inter-company)
The following lines come from FI screens defined in Customizing and related to coding block (*) Dynpros from function group KACB, not only for P.O. but impact possible on whole FI/CO transactions.
Regards,
Raymond
(*) SPRO : Financial Accounting ... Edit Coding Block (OXK3) and Define Subscreens for Coding Blocks (OXK1) -> First step is read the Customizing documentation and ask funciionals for impacts.