How to make cases non editable once the cases are marked as closed?

Updated 

This requires additional implementation to be done.

Once a case is closed, agents will not be able to reply to that case, change custom field values, apply macros, and take actions from the message options icon. Note that you can also give EDIT NON EDITABLE CASES permission to desired users to give them the permission to edit. To learn more about getting this capability enabled in your environment, please work with your Success Manager.