Cal. PCC § 20455

(a) After construction has begun, the legislative body, or the superintendent of streets if authorized by the legislative body, may order changes in the work without the necessity of a hearing. The order shall be in writing, and the amount of any change ordered shall not exceed five thousand dollars ($5,000) when the total amount of the original contract does not exceed fifty thousand dollars ($50,000), nor 10 percent of the amount of any original contract that exceeds fifty thousand dollars ($50,000), but does not exceed two hundred fifty thousand dollars ($250,000).

(b) For contracts whose original cost exceeds two hundred fifty thousand dollars ($250,000), the extra cost for any change or addition to the work so ordered shall not exceed twenty-five thousand dollars ($25,000), plus 5 percent of the amount of the original contract costs in excess of two hundred fifty thousand dollars ($250,000). In no event shall any such change or alteration exceed one hundred fifty thousand dollars ($150,000).

(c) The limitations on the cost of changes permitted by this section shall not apply where (1) the change is requested in writing by the owner of property subject to assessment for the improvement under construction and the nature of the change requested is such that the cost thereof will be assessed exclusively against the property of the person requesting the change, or (2) the change in the work will not adversely affect the benefiting property and any increase in the cost resulting from the changes will be paid by the city and will not be assessed against the property within the assessment district.