R12: How to change a project number on a purchase order that has been paid

What is the recommended process from Oracle for changing a project number on a purchase order that has been through the process of being approved, receipted, matched and paid.

Unfortunately when Managers are reviewing their expenses they notice that purchase orders have been processed to the incorrect project numbers and it is too late for us to amend the order after it has been paid.  Currently we are completing a journal entry to correct the general ledger number but this change does not correct the project number which makes reporting in project costing inaccurate.

Is there a way to make a change that will correct the project? I'm guessing either in Project Costing module or the Purchasing Module?