connection-url is in a -ds.xml file, not jbosscmp-jdbc.xml. There is ManagedConnectionFactoryProperties read-write managed attribute in ManagedConnectionFactory MBean where you could change the value. But I haven't tried it.
Thanks for the answer,
Im looking at the jmx-console and the property value for ManagedConnectionFactoryProperties is chopped its : "<config-property name="
Whats the MBean for jbosscmp-jdbc.xml ?