What you want to do is stay with the stock tune. And custom tune from there after the nitrous kit, you might have to delay the timing if you pick up knoking from a sendor your shop might have this.

This is what is like to use nitrous:

wet system on the corvette DynoTune Wet Kit 150HP shot from http://www.dynotunenitrous.com/store/Scripts/prodView.asp?idproduct=206