Well, enabling/disabling logging is normally something you do by the logging configuration (setting log level).
Though you might also use JMX and register your Beans in the MBeanServer to call whatever method you like from outside JBoss (ie by JConsole or any other JMX client). But be aware, every Bean instance has to be registered, so speaking of EJBs there might be multiple. I once solved this by having one Singleton EJB for every SessionBean working as the MBean serving/saving parameters and informations from every instance.