I'm not exactly sure what you're asking for here but it sounds like you'd like to add a page to your site that uses a different layout than the theme's available header type layouts (e.g., header, no header, splash, landing). If that's the case, you can create your own custom header type layout presuming you know how to code html. You can start with a copy of an existing header layout (copy the entire html code for that header) and then modify it the layout as needed.
To access the html code for the theme's available header types, in the Site Editor, click "Theme" in the top menu navigation, click the "Edit HTML/CSS" button in the left-hand sidebar, and then click on any of the "Header Type" layouts to see the code. You can modify an existing header type or create a new header type layout by clicking the "+" sign to the right of the "Header Type" label. You can populate the custom header type code window with the html that will give your custom header type the page layout you desire. Again, it's easiest to start with a copy of an existing header type layout html so just choose an existing header type (e.g., header.html), copy all the html, paste it into your custom header type and then modify the html as desired.
