Create a layout template based on existing template
To create a template based on other template:
    - In the main menu of your website’s backend, click Design » Page Templates.
 
    - Click Create a Template.
 
    - In Name input field, enter a name for your template.
 
    - Select Use template and click Select another Template.
 
    - From the window, which appears, click a template, which will serve as basis for your new template. 
 
    - Click Done.
 
    - Click Create this template.
    Your new template opens in the Layout editor, where you can divide and reorder the blocks as you desire.  
NOTE: Rules for nested templates:
    - Changes of a template are applied to its child template.
 
    - You cannot edit the parent template while editing the child template.
 
    - If you delete a template all of its child templates and all pages that uses this template will be deleted.
     
 
RECOMMENDATION: When you create a nested page template, based on a layout file, we recommend that you select the MVC only option, as there may be potential issues in Web forms or hybrid modes.