When a new row is added to the grid, some columns should have already default values. In my example caseID, CustomerID columns are filled automatically. The CustomerId comes from the previous screen. And the CaseID, current working application's caseID.
Save as the "pyPreGridUpdate" (Available in @baseclass) activity to your class and customize it your application rule set. The activity provides many actions like when row is added, deleted etc..No additional configurations required to the grid.