Where do you work?
Where do you vote?
Where do you pay income tax?
Do you have a CA license?
See Cal. Veh. section 516
How often is your car operated in CA?
cal. Veh 4004.4
If the vehicle is operated more in CA than any other state, EVEN if you are a Nevada resident, you must register in CA.
More to the point, in your post, you advocated getting a P.O. Box, not a residency, which is easily seen through. That is a criminal violation of Vehicle Code section 8804, a misdemeanor for evading fees and taxes, punishable by up to 6 months in the county jail.
And, yes. California cares about this a lot. So much that they have created a snitch website. https://www.chp.ca.gov/Notify-CHP/Cheaters-Out-of-State-(Out-of-State-Registration-Violators)
Piss off your neighbors? They may just report that out of state plate they see pull up to your CA house every night.
Some of this changes if you're in the military.
This stuff may be somewhat difficult to prove (though not that hard if you admit or a neighbor snitches you out), but it will require hiring a criminal defense attorney and having a misdemeanor hanging over you.
This isn't to sya that registering at a non-SMOG address isn't illegal. It is. But no one will really care and your neighbor won't know he can snitch you out.
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I'd also note that passing a SMOG sniffer on an AWD car is easy. A warmed up catless car might squeak by on a good day. It doesn't actually mean your exhaust is clean.