I didn't like the fact that all of my JWS applications have a launcher named "launch.jnlp" so I added the Task a property named "jnlpfilename".
So it's possible to set the name of the launcher:
<jnlpwar jnlpfilename="myApp.jnlp" offlineallowed="true" ...../>
Eclipse patch that adds the property "jnlpfilename" to the task