The question:
Is there some way to \"connect\" to a running JVM and change system properties (given by -Dproperty=value) without stopping the JVM and without having programmed a
As others have already suggested, probably can't change the system property value used by your application. One option might be restarting your application. It seems that Jboss offers JMX enabled stop/start ability for web applications which you can read here though I haven't actually tried it out.