Client had to do it manually due to time constrictions, but I'm still curious about being able to do it.
Here was this situation - invoices imported thru SO in this case used /CREDIT as line item (so doesn't matter if SO or AR). The invoices also import in the deposit field because they are all paid (or debited in this case) by credit card so we want a zero balance.
BUT the folks who create the file for importing screwed up this file and the field that was used for the line Extension was accidentally 0. So the invoices imported with a /CREDIT line with 0 amount, but imported in the full (negative) deposit. The invoices are sitting in AR with a balance because of the deposit field.
So what I wanted to do was to import just a /CREDIT line with the appropriate extension as an adjustment on the invoice, so it would zero the balance in AR (and also post correctly in GL, since we had a posting to AR when we shouldn't have had one, had the balances been zero).
But any import I tried told me either I had to have lines, or something about the invoice number being invalid, although it also showed me that it was a duplicate invoice number. I had Adjustments set to Y, but obviously that didn't matter (I moved it to the very first field, too, just in case).
Have another client where it would be helpful in AP on a mass adjustment basis, too, to be able to import in AP Invoice Data Entry adjustments, not new invoices. Since the Adjustment field is available, I don't see why they haven't correctly written the imports to allow you do to this.