Is it permissible for an agent to disburse zakat to another person who is more in need, but not specified by the principal, instead of the person designated by the principal?

The agent is not permitted to contravene what the principal has stipulated for him, because the agent's actions are restricted by authorization. If the agent acts contrary to what he was authorized for, there is a dispute among scholars as to whether he is liable for what he disposed of without the principal's permission or not. The more correct view is that he is liable, as mentioned by Ibn Abidin and the Permanent Committee. He is obligated to re-disburse the money and distribute it to those specified by the principal, unless the principal approves his unauthorized action.