No.
Once a PO has been created and pulled into SCView, we cannot cancel or delete a PO. If a PO is deleted on the USAS side, it will still exist in SCView as an archive record of what happened with that PO number.
If you decide to convert a different requisition under the same PO number, you can use the "Refresh PO from USAS" button located in the Purchase Order manager to pull the new PO image into the file.