You can change the background image and logo.See Customizing Magellan
You can change the look and feel of your site with CSS. See Changing the look and feel of your site
Edit Siteconfig.json to manage the controls on the generated site. See siteconfig.json
The Json files in C:\Magellan\Templates\Magellan\assets\resources provide the texts that are displayed in all the generated headings and textblocks.This includes the texts in all localized variants of the site.
There are many, one for each language, edit the text to suit your needs.