California Law Regarding Change Orders
In the section of the proposal/contract regarding change orders offered by many contractors, it's stated using words to the effect that; "No extra or change-order work shall be required to be performed without prior written authorization and signed by both parties prior to the commencement of any work covered by the new change order. The order must describe the scope of the extra work or change, the cost to be added or subtracted from the contract, and the effect the order will have on the schedule of progress payments (if applicable) or the completion date."
California law does say that a change order must be in writing for all public projects, and that in private projects, the change order can be either verbal or written.
While the law does say that change orders should be in writing, if the project owner for a variety of reasons has verbally agreed to forego written change orders (on a private project), they could be in effect setting a precedent. In several cases, where verbal change orders have led to disagreements and contention between and the project owner and the contractor, the court in each matter has been left to decide.