Go ahead and make all your design updates in the Edit Layouts mode, creating the exact layout that you want to reuse. When you are finished, choose to Apply and Save to My Layouts so you will be able to select and use it again for other pages.
When you want to apply this custom layout to other pages, go to the page you want to apply it to and select My Page Layouts from the top left of BookSmart.
All of your saved layouts will appear in My Page Layouts. Click on one you wish to apply to the current page.
Layouts saved in your My Page Layouts will appear for any new books of the same size that you start in BookSmart. For example, custom layouts that you have saved for a 7x7 book will appear in other 7x7 books that you create, but in not in 8x10 books.