This is disingenuous; you have to do a lot more than change an air filter. You would have to change the actual piping, etc. with one that the seller declined to spend the money on certifying as compliant.

Further, and most people don't know this is a thing, you CAN tune your car as much as you want and have it certified with all of those parts as a one off for about $5,000 and a six-ish month wait. This is how you can legally import overseas vehicles and get a California title and registration, but it's $5,000 per test, and it usually takes more than one if you aren't super prepared. After the certification the entire engine (including all modifications) are regarded as that being the SMOG compliant form.

One other major loophole is kit cars; SB100 allows for non-SMOG vehicles to be built as a kit. Not everyone's cup of tea, but you can build things like the Superlite GT-R [0] or SL-C [1] and never SMOG it.

0: http://www.superlitecars.com/gtr/

1: http://www.superlitecars.com/slc