Overview of Creating Custom Site Definitions
Published: May 2010
This topic provides an overview of creating custom site definitions, including site definition configurations, which are a part of site definitions.
To create a custom site definition with one or more custom site definition configurations, follow the procedures in How to: Create a Custom Site Definition and Configuration.
Modifying site definition files to customize existing sites or lists is not supported. These files may be overwritten when you install updates or services packs for Microsoft SharePoint Foundation, or when you upgrade an installation to the next product version. A good guideline is to use the object model to modify sites after they are created.
When you are modifying site definitions, be aware that the contents of pages that were customized in Microsoft SharePoint Designer are stored in the database. If, during the process of creating your custom site definition, you modify a page in SharePoint Designer, changes that you later make to the definition may not affect the page.