[Duece McCracken]

tuners dont mess with emissions stuff because they can get in legal trouble. see harley davidson screaming eagle tune fiasco.

Ummm all tuners turn off the rear O2 sensor with a full tune or an ots stage 3 tune. You have to request for it to be turned on last time i checked.

Which is due to the nature of aftermarket downpipes, either catless or high flow thus causing the emissions code.