I appreciate the detailed information you provided regarding the Purchase Order in QuickBooks Online (QBO), BriOz84. Allow me to assist you in this matter.

Please note that if you change the amount of the bill when converting the PO, QBO will automatically treat the conversion of the PO as fulfillment.

To keep the status of the PO open,  we can adjust the total amount by modifying the quantity. For single-item POs, you can manually calculate the equivalent quantity based on the total amount and enter the decimal value in the QTY column.

Please refer to the screenshot below for reference:

If there’s anything else you need, please don’t hesitate to reach out.