Yes, the tune would have to be changed back to stock unless you want to run race gas. The tune adds timing, which requires more octane, and the nitrous requires more octane because it burns faster. If you are running 91-93 premium pump gas, you won't have enough octane to prevent detonation and could cause engine damage. The simple answer is to remove the diablo tune and run premium on the stock tune when you plan to spray.
I would definately run a WOT switch. That combined with a Window switch will be very safe.
I never worried about purging the line. The effect is only a few hundreths of a second in ET, and only on the first time you spray after openning the bottle.
When you see the professional racers making a big long purge... it's probably because they purposely warm the bottle to have excessive pressure, then purge until the pressure is exactly where they want it. In this case, the nitrous stays warm and helps to maintain bottle pressure over the run, compared to a bottle at the standard temperature which will allow bottle pressure (and performance) to dip during the run.
So in short, don't worry about a purge. It would be much more useful to have a bottle heater.
I don't have a bottle heater and don't worry about it. If I plan on spraying, I just put the bottle in warm water to warm it. That warms the liquid and the gas on top. If it's cold outside, I'll wrap the bottle in a coat when I put it in the car. Works just fine for the trips to the track.
sorry i guess thats not in my sig but i have drag radials for the track that i use
also i def want to have a window switch too
so i do have a diable tune on my car right now so would that have to go? its not a custom tune just there "performance tune"
also u are really able to run a 100 shot with absolutly no tune change over stock tune?
also do i need a purge valve or WOT switch? if not how do u purge lines and all?
