CA's version of EPA is CARB. There is no update requirements for any Diesel engine in the state...OEM for the year of mfgt is the only expectation.
And, since there is no emissions check for Diesel engines in vehicles with a GVWR over 14,000 lb, there are no controls on owner modification for RV's
https://www.dmv.ca.gov/vr/smogfaq.htm
Safe travels