Hi Paul,
you shouldn't (need) to play with the JBossWS integration deployment aspects. Your additional deployer (DeploymentUnitProcessor (DUP) in AS7) would likely live in the AS7 XTS subsystem and use the JBossWS SPI to modify the org.jboss.wsf.spi.metadata.webservices.WebservicesMetaData that is created during Phase.PARSE of AS7.
I would wire that new DUP into the deployers chain after the Phase.PARSE_JBOSS_WEBSERVICES_XML, so once the WebservicesDescriptorDeploymentProcessor and JBossWebservicesDescriptorDeploymentProcessor have run. Those two basically create the WebservicesMetaData into the deployment unit if a webservices.xml is found in the deployment. You'd need to update that object or create it if the webservices.xml was not in the deployment. Once that's done, the jboss-as7 / jbossws deployment can go on as is and your additional info will be considered.
If you want to have get an idea of the DUP that are involved in the ws part of the deployment process, the class that adds them is org.jboss.as.webservices.dmr.WSDeploymentActivator