Let's start by creating a invoice for a stock part called 'Door Frame':

INSERT INTO "InvoiceLine" ("CustomerRefFullName", "RefNumber",
"InvoiceLineItemRefFullName", "InvoiceLineDesc", "InvoiceLineQuantity",
"InvoiceLineRate", "InvoiceLineAmount", "InvoiceLineSalesTaxCodeRefFullName",
"FQSaveToCache") VALUES ('Richman, Karen-2273526', '1001',
'Door Frame', 'standard interior door frame', 3.00000,
150, 450.00, 'Non', 0)

To retrieve the TxnID for the transaction I just created I use the QODBC stored procedure:

SP_LASTINSERTID invoiceline

I can then retrieve the TxnLineID for the invoice line using the TnxID: '5DE5-1197763322':

select TxnID, InvoiceLineTxnLineID, InvoiceLineSeqNo from InvoiceLine
where TxnID='5DE5-1197763322'

The TnxID and TxnLineID for the Invoice line I just created is: 5DE5-1197763322 and 5DE7-1197763322

In QuickBooks a quick report for the invoice I just created shows the income account to be: Construction:Materials

Using the TnxID and TxnLineID for the Invoice line I just created I can change the income account to a new Income Account by using the following UPDATE statement: 

UPDATE InvoiceLine
SET InvoiceLineOverrideItemAccountRefFullName = 'New Income Account'
WHERE TxnID = '5DE5-1197763322' AND InvoiceLineTxnLineID = '5DE7-1197763322'

When I refresh the Quick Report in QuickBooks, it now shows the Income Account as: 'New Income Account':