VM 2.0.26d can not edit a price anymore even.
vmError: updateSingleItem and UPDATE `#__virtuemart_orders` SET `order_total`=(SELECT sum(product_final_price*product_quantity) FROM #__virtuemart_order_items where `virtuemart_order_id`=30843)+`order_shipment`+`order_shipment_tax`+`order_payment`+`order_payment_tax`+0, `order_discountAmount`=(SELECT sum(product_subtotal_discount) FROM #__virtuemart_order_items where `virtuemart_order_id`=30843), `order_billDiscountAmount`=`order_discountAmount`+0, `order_salesPrice`=(SELECT sum(product_final_price*product_quantity) FROM #__virtuemart_order_items where `virtuemart_order_id`=30843), `order_tax`=(SELECT sum( product_tax*product_quantity) FROM #__virtuemart_order_items where `virtuemart_order_id`=30843), `order_subtotal`=(SELECT sum(ROUND(product_item_price, 2)*product_quantity) FROM #__virtuemart_order_items where `virtuemart_order_id`=30843),`order_billTaxAmount`= WHERE `virtuemart_order_id`=30843
I have no 2.0.26d, but with latest test version which will be the next stable version is no problem with order editing.
I still have a 2.0.26d test site - BE order price edits work OK for me. No errors.
Prices have been editable for ages and works, but still the ability to add an order line to the order is not included as a useful functional option?