According to the International Standards for the Professional Practice of Internal Auditing (Standards) issued by The Institute of Internal Auditors (IIA), the Chief Audit Executive (CAE) must communicate and obtain approval from the board for significant changes to the audit plan. A corporate merger is a significant event that introduces emerging risks, necessitating an interim adjustment to the audit plan. The CAE's responsibility includes ensuring that the board is informed and approves the revised audit plan to address these new risks adequately.
Reference:
The Institute of Internal Auditors (IIA) Standard 2020 - Communication and Approval: "The chief audit executive must communicate the internal audit activity's plans and resource requirements, including significant interim changes, to senior management and the board for review and approval."