Vendor performance receipt due date changes?

Occasionally we have a vendor that disputes either the due date on a PO or the Date we received it (we received physical product on a Friday and then received it on Monday and did not put Friday as the posting date, vendor was late due to something we caused ie changes to the priority or a sample run, etc and PO date did not get changed before the receipt.)

Bottom line is we need a way to change the due date/planned delivery/requested delivery date on the Purchase Receipt lines. The problem is these are protected fields in NAV and they cannot be changed in a form and the logic is deep in the core NAV programming so we don’t want to touch. Changing the posting date is not a good option either as many times it is just one line out of several on a receipt that needs the due date moved to the posting date so the receipt line is not late.

Has anyone had a similar issue or a work around? We do have options of a processing report to change the date but this would be very cumbersome for the end user. Another option would be a new custom field added to the PO and pushed to the receipt that would be the due date we use for vendor performance reporting in SQL and possibly could edit as needed on the receipt.

Any ideas, suggestions?