correct me if I'm wrong but I'm pretty sure it is required if you do not want the heavy gas smell. Tune eliminates that if I'm not mistaken (still kind of learning myself)
All the tune does is get rid of the CEL from cat system under efficiency. You will still get a heavy gas smell because there is no longer a super hot catalyst to burn off vapors.
however some people have had luck running anti foulers on the rear 02 sensors and have not had a CELight.
For the short term just run it as is and deal with the light (Short term)