Cal. Gov. Code § 19575.5
At any time before an employee's appeal is submitted to the board or its authorized representative for decision, the appointing power may with the consent of the board or its authorized representative serve on the employee and file with the board an amended or supplemental notice of adverse action. If the amended or supplemental notice presents new causes or allegations the employee shall be afforded a reasonable opportunity to prepare his defense thereto, but he shall not be entitled to file a further answer unless the board or its authorized representative so orders. Any new causes or allegations shall be deemed controverted and any objections to the amended or supplemental causes or allegations may be made orally at the hearing or investigation and shall be noted in the record.
Ca. Gov. Code § 19575.5