I am not 100% sure but I think that the class_identifier means the class the contains the XML block which is viewed using this template. The class_identifier of the embedded object does not matter.
I believe that you have problems with the path used in your override rule. Yo have to be sure that the actual tpl you want to use is in <your_design>/override/templates and then inside the path you put into your override definition.
This is an example of an override rule we use in one of our sites for embedded images:
