Do some googleing on the topic. I’ve read about the hot cat and also about adding a large percentage of ethanol to the fuel.
I live in Santa Cruz county and we don’t have these “dyno” type smog requirements here. Even my 14yo ford truck passes with flying colors. Not sure why you’re so close on yours. An exhaust upgrade won’t effect your smog output.
O2 sensors OK? If they have 100k or more miles on them, best to replace at least the pre-cat sensors. Even tho they don’t throw a code, they can be inefficient and cause your car to run rich. You can google on that too.