Well i havent done this on my Koup (nor will I) but I can go off of experienceAll legal aspects aside, what are some of the pros and cons of getting rid of the catalytic converter? In specific, sound and performance wise. I'm considering doing this, but want to hear about personal trial and error from everyone else first.
Most, if not all, cars built today use a second HO2S sensor behind the Cat that monitors the exhaust continuously -- if you use the resistor you are referring to you, will still get a SES/CEL because the ECU will detect a constant signal and not a fluctuating signal within prescribed parameters.Get an High flow Cat from TurboKit!!!
As for check engine light you could buy some MILS eliminator (some sort of resistor that give constant signal to your ECU from O2 sensor)