It is not possible to add cache store/loader to the existing cache. There is no operation available for that (as it used to be for JDG 6.6.x version).

You can find the running JON server with latest JDG library and server plugins installed (7.1.0.CR3) here:

http://10.16.23.101:7080/coregui
username/pass: rhqadmin/rhqadmin

UPDATE:

I have also tried the other way: I have added e.g. a file-store element to the one of the existing caches directly from the xml configuration, restarted the server so that it is reloaded in JON UI to see what will be the view. But there was no difference.