AR Invoice Quantity Field Not maintainable in UBAQ

I’m trying to build a Dashboard to update Invoices before posting. The Price is able to be updated in the UBAQ but InvcDtl.SellingShipQty is Not maintainable. the field in the form is InvcDtl.DspSellingShipQty and not in the Table. Any suggestions or work arounds.

The quantity comes from the packing slip and cannot be changed in the invoice.

We are invoicing without a shipment. the quantity can be changed in the invoice form. It must have a process attached to it to make the change.