You may already be familiar with the concept of "skins" from other programs: You select a skin file and the appearance and layout of the entire program is transformed in seconds. Help+Manual enables you to do this with your HTML-based output. You can save your entire design with all its HTML templates and relevant HTML settings in a .hmskin file. You then select this file when you publish to apply the layout to the current project without changing any of the project's own settings.
Please note that you can only save your own projects as skins if you have the Professional or Server version of Help+Manual. Basic version users can use skins without limitations and edit existing skins (for example skins from the Help+Manual Plus Packs) but they cannot create new skins from their own projects.