You may need to create a new page that will be similar to existing pages, but with some minor modification of the page template. Imagine you want to display the editable region from the previously created page template in a container box.

 

Instead of creating the page template from scratch, simply create a new page based on your existing page template.

 

 

Then choose the page, click Properties -> Template, click Clone as ad-hoc template and click Save. A new ad-hoc template is now created and you can edit it without modifying the existing pages based on the original template:

 

 

Now switch to the Design tab and click the Configure () button of the Editable text web part. Select the Black box container from the Web part container drop-down list and enter What's new into the Web part container title field:

 

 

Click OK. Switch to the Page tab and enter some text into the editable region. Click Save and click Live site in the main toolbar. You will see a page like this:

 

 

As you can see, the text is now surrounded by a black container. When you check the original My test page, you will see it uses the original design and it wasn't affected by the change we made to our new copy of the page template.