I went to the exhaust shop today and the guy said that if I replace the cat with a resonator that the computer will throw a code because of the rear O2 . Wouldn't punching the cat do the same thing? Do tips make a difference in sound or ae they just cosmetic?

Knocking out the CAT should throw a code too. I know the big ugly a$$ rice tips provide some sound, LOL, but tips that WE would get may not. Some tips are different though. I know some are resonated too which may sound different than plain rolled tips. But I don't have mine yet so I'm not the best one to tell you.