To the BEE editor, there is no difference between messages and templates.
BEE receives a JSON file when the editor is initialized, and returns the updated JSON file and its HTML translation when the message is saved. So, to BEE, both a message and a template are just a JSON file that was "passed" to the editor.
Of course, there is a difference between templates and messages in terms of the user experience in your application.
For more on this topic, please see: