As long as your centered over your sidecut, you'll be good. Don't push your stance on boards with setback too forward otherwise you'll be ahead of the waist on switch and in front of the tails flex point while regular. IMO I wouldn't tinker with it too much or at all, as switch is just a matter of practise, centering a stance on a directional board isn't going to make you learn any easier. It's just going to make your tip & tail the same length, off center your stance with the sidecut and flex pattern of the board...
I would say this depends on your progression.
While you're learning, the sidecut shape does not matter as much because you're not going to be carving a whole lot of your riding...at least not to the point where the "sidecut profile" really matters. If your board is directional, it likely has a significantly longer nose than tail. Therefore, when you are performing SKIDDED turns, riding switch will be harder because there would be more rear edge to drag on the snow...making it harder to turn. It's the basic principle of leverage, where you would put your hands more toward the end of a tire iron to producing more force on the nut. So it would take more work to skid the board. You can definately feel it, especially when you're much better, which is why they make twin boards.