Hi,
If subsequent documents are posted, system wont allow to change the delivery cost conditions in PO.
If the delivery cost invoice is not entered, you may enter the planned delivery cost in MIRO - Planned delivery cost option and change the invoicing party in the MIRO-header - Details tab and post the invoice with the applicable conditions.
If the delivery cost invoice and payment is done to wrong vendor, then you may cancel these docs and enter the invoice again in MIRO-planned delivery cost with correct invoicing party as mentioned above.
Regards,
AKPT