Cal. Gov. Code § 11507

At any time before the matter is submitted for decision the agency may file or permit the filing of an amended or supplemental accusation. All parties shall be notified thereof. If the amended or supplemental accusation presents new charges the agency shall afford respondent a reasonable opportunity to prepare his defense thereto, but he shall not be entitled to file a further pleading unless the agency in its discretion so orders. Any new charges shall be deemed controverted, and any objections to the amended or supplemental accusation may be made orally and shall be noted in the record.