Starting in September 2013, the ability to customizate Notes web has been added to SmartCloud. To do so, you use an Extension Forms File, just as with on-premises IBM iNotes. But you would need to download the template from SmartCloud. And then have ISSC check it and install it for you. Once it's on SmartCloud, you use the Admin UI to apply it to your users.
See this article
in the SmartCloud documentation for details.