The DDT drivers are read-only connections to the data records so, within those drivers, you cannot update the spreadsheet. I would suggest using a check point or some other means so that, when the loop is done, you verify the existence of the new order and log it to the TC Test Log rather than writing it out to the DDT data source. As a general rule of thumb, updating your data source used for executing a test as part of the test "damages" the reliability of the test because then the data source is no longer in the state it was when the test was executed.