When attempting to register a xa datasource via the management api I ommited driver-name and the operation failed. After adding the required attribute and re-sending I now get:

failure-description" => "Operation handler failed: org.jboss.msc.service.DuplicateServiceException: Service jboss.xa-data-source-config.java:jboss/datasources/myDS is already registered",
[ERROR] "rolled-back" => true