Cal. Pub. Cont. Code § 20447

Unless the power to proceed shall have ceased at the conclusion of the hearing on the resolution of intention because of a majority protest, at any time before the confirmation of the assessment the legislative body may make changes in, to or from the boundaries of the proposed assessment district, the work proposed to be done, or any act, determination or provision made, or permitted to be made, by the legislative body under and pursuant to this division, which act, determination or provision does not affect the jurisdiction of the legislative body to order the work or improvement; provided, that after the award of the contract no such changes shall be made without the written consent of the contractor or the bidder to whom the contract shall have been awarded. The legislative body shall not change the boundaries to include any territory which will not, in its judgment, be benefited by the work.