Not sure how AS7 + OSGi behave, it could be rather a question to ask to the AS7 forum as this is probably not that related to Eclipse debugger but rather to how the JVM/AS/OSGi behaves.
That said you could give a try to JRebel from Eclipse or JBoss Developer Studio. It generally allows more modifications during debug. See documentation here: http://zeroturnaround.com/software/jrebel/jrebel-how-to-using-jrebel-with-jboss-developer-studio-and-jboss-as-7-1/
HTH