Supported and unsupported scenarios for working with custom site definitions and custom area definitions in SharePoint

I don't really like this Microsoft KB - it is amazing how limiting it is - Supported and unsupported scenarios for working with custom site definitions and custom area definitions in SharePoint. It seems that Modifying site definitions - changes in Onet.xml , adding AllUsersWebPart element is an unsupported scenario as well... too bad. PS It seems that some people share my opinion - see SharePoint custom site definitions... I'm lost...sharepoint