Currently Being ModeratedJun 24, 2013 9:08 PM (in response to Dave Fynan)
All you need to do is import the additional code sheet "ontop" of the original. You should never need to modify the excel spreadsheets.
Click on Apps
Click on grey oval showing remaining codes for an app you would like to add codes to
Click on import codes
Select the NEW (additional) code sheet you have downloaded for that app
You should now see the total available app codes increase by the number of additional codes you purchased.
Hope this helps!