The "Clever Item Tracking Plus Setup" page stores the default Reason Codes to be used for Sub-lotting and changing expiry dates within the app. 

On opening this page, there are 2 fields. The Default Sub-Lotting Reason Code has a dropdown lookup to the standard BC "Reason Codes" table. Select the "Reason Code" you want to use when creating Sub-Lots. These can be changed at the time from the "Lot No Information List" page but choosing an option here will default the reason Code at the time to save manual entry. 

Now from the dropdown, choose a Default Change Expiration Date Reason Code from the same list. Again, this can be changed when changing the expiration dates from the "Lot No information list" page but choosing one here will default the Reason Code at the point in time. It can be overwritten.