With the stage 1+ and Stage 2 files, we receive the base file, which is already calibrated to our climate and fuel. We then log the car, taking readings such as afr's etc, we also sometimes do a dyno run. All this info is then sent to my technician and he writes the file accordingly. We load the revision file on and log again.
We generally advise the customer to do the hardware mods first, but if a stage 1 file is loaded and the customer then puts exhaust, we do a revision file for the exhaust. It is done the same way as above. It is not necessary to retune the car if small mods are done, generally if a turbo car is tuned and then the customer changes exhaust, we do a revision.
Hope this clears it all up?
Sabertooth: will have an answer for you soon.