Retro fitting, in the field, was common practice especially in the luftwaffe. I know some modellers are sticklers for detail and being authentic. But as another member quite rightly said, this is modelling and thus open to any ideas or alterations one wishes. As long as you have fun thats all that matters... In my experience many German fighters were adapted over the years. Plus the range of add on field kits in the luftwaffe was very commonplace. Certainly with fighters/fighter bombers...