Additionally, you can use the following velocity code within the custom field to restrict editing to users with the role "CMS Administrator." Thanks to Chris Falzone for the velocity code.
#set($session = $request.getSession())
#set($user_id = $session.getAttribute('USER_ID'))
#set($user_obj = $cmsuser.getUserByUserId($user_id))
#set($user_map = $cmsuser.getUserProxy($user_obj).getMap())
#set($user_roles = $cmsuser.getUserRoles($user_obj))
#if(!($cmsuser.isUserRole($user_obj, 'CMS Administrator')))