So you make your changes and now you want to redistribute the plugin. As with any other Eclipse plugin, you have to export it as an eclipse plugin. It is very easy...
TODO. this is documented at : http://j2s.sourceforge.net/setup-j2s-from-subversion.html. this is what it sais:
Export the above 4 projects as "Deployable plug-ins and fragments". For example, you may select C:\eclipse as the directory of export destination. Project "net.sf.j2s.ajax" and "net.sf.j2s.lib" must be exported with "Package plug-ins as individual Jar archives" UNCHECKED. And project "net.sf.j2s.ajax" should be exported with "Include source code" option CHECKED, so later you can bind sources much easily.