So should I bother installing cats?
If you wanna pass the smog test you'll need cats. You won't pass the sniffer test without them. After you pass the test you'll be good for 2 years until the next test. Ted May can set you up. How long do you plan on staying in the PRK?
Technically speaking, you're right, you have 20 days to register after bringing the car into the state. You can take your chances and keep driving on the NY plates. If you get stopped and tagged it'll be a fix-it ticket. Then you'll have to install Cats, pass a smog test and go to the DMV to get it registered. Any business at DMV, make sure you make an appointment otherwise you're looking at standing in line for a long time.
You have to apply for a CA Driver License within 10 days of establishing residency. The operative word is
residency.
Read 12505 CVC and see if there are any loopholes for you.
Residency
12505. (a) For purposes of this division only and notwithstanding Section 516, residency shall be determined as a person's state of domicile. "State of domicile" means the state where a person has his or her true, fixed, and permanent home and principal residence and to which he or she has manifested the intention of returning whenever he or she is absent.
Prima facie evidence of residency for driver's licensing purposes includes, but is not limited to, the following:
(1) Address where registered to vote.
(2) Payment of resident tuition at a public institution of higher education.
(3) Filing a homeowner's property tax exemption.
(4) Other acts, occurrences, or events that indicate presence in the state is more than temporary or transient.
(b) The presumption of residency in this state may be rebutted by satisfactory evidence that the licensee's primary residence is in another state.
(c) Any person entitled to an exemption under Section 12502, 12503, or 12504 may operate a motor vehicle in this state for not to exceed 10 days from the date he or she establishes residence in this state, except that he or she shall obtain a license from the department upon becoming a resident before being employed for compensation by another for the purpose of driving a motor vehicle on the highways.
Go
HERE for the most confusing reading you'll ever experience.