I have just commited a JMX console based on nukes which is imho way better than the actual one.
You can change mbean attribute individually. XML is supported (the document is in the text field). You can change the type of an argument or set it null explicitely. Model mbean are supported, that means you can edit descriptors (just change values) Notifications info are displayed. You can unregister mbeans.
It will work with nukes + jboss-3.2.1 (unfortunately, we don't support head and we don't have branches in the cvs modules).