This form is for entering charges to a customer (Amount field). There may be existing charges that will populate the grid. The intent is not to change the custno but to populate a new row with the custno/subno and agent (name) of the customer to be charged in that row and then assign an charge amount.
You raise a good point that I should set any existing charges entered into the grid to read only / non-editable.
Based on your previous suggestion I disabled editing on the other columns using:
e.Layout.Bands[0].Columns[“var”].CellActivation = Activation.NoEdit;
and just used the events to write those values.