Outbound Delivery is created by a different team. They do not know the freight forwarder/carrier.
Once the Outbound delivery is created the warehouse guys, picks the good from warehouse and clicks on the PGI button.
The requirement is to add the partner function for freight forwarder/carrier with which they are issuing the goods.
Ideally adding a new partner function should be disabled after doing PGI. What can be the reason for it being disabled before even PGI is done. There should be provision to add- new partner function in change mode.