Yes Steve,
You are correct. If you want to duplicate or replicate a completed PO, then you change the runtime variable to edit completed PO's and you will be able to duplicate or copy a completed PO to a new Order.
In this situation, the location code would also have to be revised for the line items. Then as you suggested, receipt the new PO, and credit (return) the completed PO (for the wrong location), to correct the quantities by location.
The only hitch is that you will have to take both the credit and the receipt on the duplicated order into AP and offset there. We do not have the function that allows you to combine a credit with a receipt.
You can duplicate an existing open PO without modifying the edit completed PO's. You could also duplicate recurring PO's by creating a PO template.
Brian