When a PO is activated, the estimated price in a line item is encumbered. It is possible to change this price after activation.
Change the estimated price in the line item.
If you click somewhere else on the page, you will see (PO already activated) next to Activatable.
Reload the page and you will see the encumbered amount for the PO change and the new price remains in the estimated price box.
If you check your fund and are able to identify the item (not easy as the fund details don’t display a line item ID) you will see that the Encumbrance amount has changed to the new price and that the Origin Amount remains the original price. The entry moves to the bottom of the list. The create time remains the same.