Is the dual switching on the same circuit? Inner Row/ Outer Row switching (2 ballasts), or BiLevel (one Quick Step Ballast). If it is a quick step ballast, I would not change anything except for the switch symbol.
If they are on the same circuit (2 ballasts), the load would still remain the same. If different circuits (still 2 ballasts), then you would need to modify the fixture family (add another connector) to account for the different loads on each circuit.