Your asking about California, the most "anything you do to your car is illegal" state? C'mon. If you really want to find out for sure, talk to a reputable inspection facility. They are the ones that are going to fail you or not
Well you would have to see if they have a CARB EO number.
But if you want to get technical, it is illegal to remove a functional catalytic converter under 50k miles....so even if you put a cat system on the car, they could bust your chops if they want to. Most don't and if you have your EO numbers and you can pass the sniffer, you will be ok.