Answer: Not exactly, you cannot add new styles or themes within Web Creator's library,  but it is possible to create page templates ready to receive content. 

Create a page and create as many copies of it as one wants by using the Duplicate function in the Project pages tab. Simply add specific contents to the new pages, and make sure to give each name a significative name when creating a copy, because changing the page names later on is not recommended. 

For example: 
You could have 'Product' template page, and use it to create a specific page for each line of products, such as clothes, gear, shoes, bags, etc. 
Each product page should have a specific name and title, and you may even give each page a set of specific metatags to help search engines identify its contents. 

Only pages that other pages link to will be included to the generated files of your website. So if you don't create any link to your template page, it will only exist in the Web Creator project, and not in your final website. 

You can design your own graphic elements, and add them to the library in the 'My library' section to have a quick access to personalized elements from any page. Keep your company logo at hand for quick and efficient customization of your pages!