Best way to correct a Sales Order item price after the fact?

Hello;

I'd like to know if there are better ways / procedures to handle the situation where a manually-entered and then fully-fulfilled Sales Order (processed all the way to Customer A/R Autoinvoice generation) is later discovered to have used the wrong (too high) price for an item.  And so, a credit/refund amount is due back to the customer, because we charged too high a price on the SO Line, resulting in too high a price on the AR Autoinvoice.

Currently, we would copy the original Sales Order into a "Credit Only" return order -- requiring no Return To Supplier steps, no PO updates, etc.  In that credit-only return order, we'd modify the line in question to reflect the necessary credit amount we want.  This would flow to A/R via Autoinvoice, as a new credit memo for the customer.  However, we've found that if we do it this way, it prevents us from executing a legitimate return of those same goods, if the customer decides to actually return some or all of those same items, later on...