Update Sales Order already linked to Purchase Order

We have a purchase order created from a Buy to Order, Dropship, sales order and it consists of one line.
We have now learned from our supplier that there is a back order. So, we want to update the sales order and purchase order to reflect the correct ship dates. We “Unapproved” the Purchase Order, but when we try to add a Release and update our quantity, we get a message that the quantity can’t be changed because it is linked to a purchase order.
We ended up deleting the line from the purchase order, we could then add a release and update the quantity. We then put the line back on to the purchase order.
I’m wondering if this is best practice by deleting a line off of the purchase order.

Wonder if this is worth reporting/checking with Epicor tech support?
The sequence you describe seems obscure enough that these conditions were never accounted for on their end. Might require a fix…some day/release?