If you’re using DITA-FMx and would like to modify the formatting and layout in the topic authoring view or for book publishing, you’ll need to modify the corresponding FrameMaker structure applications (Topic, Map, and Book). When it comes time to customize the structure apps, you should “clone” the default applications provided with DITA-FMx to create your own applications rather than modifying the default apps. This video walks you through each step of this process.
This is a fairly complex topic involving the modification of the structure application definition file (structapps.fm) as well as the structure application’s EDD and template files. If you’re just starting out, it’s probably best to work with the default applications for some time before worrying about any customizations.