JRebel works only with the individual class files, and not with JARs. If you change dependency you will have to redeploy the application, unfortunately. However, there's ways to workaround.
If you can use the dependency as a source, you can then generate the dedicated rebel.xml for that module and work with it as a part of your project.
If you can't use the dependency as a source, there's one more workaround: package rebel.xml into that JAR and map it to some arbitrary location. Then extract the classes of the new version of the JAR into that location.