Sounds good. Just to get you started - Designer has a notion of profiles. A profile determines a number of things, one of them being how the save/load functionality is implemented. A profile name is a mandatory URL parameter that has to be passed to designer (for example localhost:8080/designer/editor?profile=ABC&uuid=XYZ&pp=). Each profile has it's own impl class, for example for the jbpm profile see: https://github.com/tsurdilo/process-designer/blob/master/src/main/java/org/jbpm/designer/web/profile/impl/JbpmProfileImpl.java. Each profile among other things has its own config (again for jbpm profile look @ https://github.com/tsurdilo/process-designer/blob/master/src/main/webapp/profiles/jbpm.xml) which determines what plugins etc get loaded at startup.
Again, feel free to ping me on IRC and we'll talk more.