Is a trustee permitted to appoint a successor executor if the original testator granted explicit permission?

Primary text

If a testator appoints a trustee and explicitly authorizes him to make a bequest to whomever he chooses, such as by saying, 'I permit you to appoint as executor whomever you wish,' or 'Every person to whom you entrust is entrusted by me,' the appointment of a successor executor is valid. This is because the testator consented to the judgment of the first executor and the judgment of the person he appoints. This ruling is held by the majority of scholars.