The better way is to create the html file, park it a directory and then use the include function to place it where you like it to appear. These pages are not commonly called page.html. They are usually named page.php, inc, tpl or whatever. They usually have some of the pages tags stripped. What I mean is <body> might appear in the header. No such tag in main content or footer and the closing tag </body> would be at the end of the footer. They will still load and display if you don't do that but is sure makes for a distorted "view source" and I guess it might hurt you for SERPs. I just create an html page for each section of the page I want displayed, save it for redesign purposes and then strip the tags from it and save it as a php file. Since I am far from being an expert, they may be a better or easier way of doing it.
The reason why I ask is because I just recently purchase Kayako SupportSuite owned license and would like to integrate my template into the script. Is there any suggestions on that? When you say "strip the tags", what tags are you talking about...php or html? I am very weak on CSS, however I am learning CSS, but its a slow process.
In that case I would suspect that a custom header, footer and maybe changing a few items in the css is about you will be able to do. One would need to study the contruction of the scripts to figure out what could be done. I meant stripping some of the html tags from the individual html pages that will make up your finished page.