TideSDK is no different than any web app for branding. CSS is used to style your HTML. Any default CSS you have in your base app may be overridden for branding of course.
Beyond the HTML, the native UI is controlled by the OS, and you have only the icon to be concerned with and replacing the default artwork (with your own branding) in the native installer we provide.
If you need to change the icon name, which is not a necessity, do this in the tiapp.xml and manifest. Just replace the image with one of your own. The same applies to the installer art.