[29.2. Server-side Message Load Balancing|
https://access.qa.redhat.com/documentation/en-us/red_hat_jboss_enterprise_application_platform/7.1/html-single/configuring_messaging/#server_side_message_load_balancing] contains a "Cluster User Credentials" section that warns you to change the cluster-user and cluster-password, but does not give the management CLI command. The commands should be added to the section.

/subsystem=messaging-activemq/server=default:write-attribute(name=cluster-user,value="MyClusterUser123")
/subsystem=messaging-activemq/server=default:write-attribute(name=cluster-password,value="MyClusterPassword123")