update sales data in profit segment

we have customer invoice posted from SD, reference key 1 field is updated with sales office number, later on we use fb05 to post the customer discount, the requirement is to copy reference key 1 to  sales office field in profit segment during fb05,

for example in invoice document, reference key 1 is 0123, we want subsequent customer discount to be posted with 0123 in sales office (inside profit segment)

is it possible? thanks