When you use the "default" profile, for example:
http://localhost:8080/designer/editor?profile=default&uuid=1234
saving your process will store the process .json to servlet.getServletContext().getRealPath("/repository")
and your file name is going to be 1234.json.
Next time you open the editor an navigate to http://localhost:8080/designer/editor?profile=default&uuid=1234
designer is going to try to look up 1234.json and load it if it exists.
Same would apply if we create a new profile which would store 1234.bpmn2 instead of 1234.json.
Storing the process bpmn2 in Guvnor
would be similar however the uuid of a new process would be generated by guvnor. If you want later on to edit the process, you would have to either write down that uuid or go to Guvnor, open the process there and copy the uuid from the url.
Maybe the best option would be to provide both abilities :) but figuring out which one should be first would help.