While our system was up, we entered several changes to jboss-log4j.xml manually.
The changes were made in the 'Lmited Categories' section.
One change was to raise a category priority ( from INFO to WARN)
The second change was to add new category.

The changes didn't take affect after 60 sec (or more) as configured in jboss-service.xml - RefreshPeriod entry.
The changes took affect only after jboss restart.

As I understood, jboss-log4j.xml should be polled every 60 sec and the confiuration should be updated accordengly.