California Code, Health and Safety Code - HSC § 19981

(a) All factory-built housing bearing an insignia of approval pursuant to Section 19980 shall be deemed to comply with the requirements of all ordinances or regulations enacted by any city, city and county, county, or district which may be applicable to the construction of housing.  No city, city and county, county, or district shall require submittal of plans for any factory-built housing manufactured, or to be manufactured, pursuant to this part for the purpose of determining compliance with this part or the regulations promulgated thereunder, or for determining compliance with any local construction requirement, except as provided in Section 19993.

(b) No factory-built housing bearing a department insignia of approval pursuant to Section 19980 shall be in any way modified prior to installation unless approval is first obtained from the department.

(c) No factory-built housing shall be in any way modified during installation unless approval for the modification is first obtained from the local enforcement agency.