I would suggest just editing the existing data/conf/default-object.xml file. If you include your *.war files within jboss-portal.sar, you can reference your portlets from within there. Or you can define your portlet locations within your own *-object.xml file.
If I read your question correctly, I think what you are asking is if you can add a second *-object.xml file to data/conf. Well, when you did it, what happened?