Template Documents
When you create a new document, it is typically blank. You can change this, by saving a pre-configured template document in your project's directory.
Every time a new document is created, the editor checks whether such a template document is present, and if so, clones that instead.
For the editor to find your template document, it has to be stored in the sub-folder Editor/DocumentTemplates and has to have the name Default. The file extension of course has to match the document type.
So for example if your project is located under C:/MyGame then to create a custom scene template, you would store a scene file under C:/MyGame/Editor/DocumentTemplates/Default.ezScene.
This can be done for any document type.