This field allows you to change what is displayed in Explorers type column
This will allow you to change the icon that Explorer displays for the file type.
Click change will allow you to select icons from:
GFTE will allow you to view all files contained in selected file
This will allow you to change the Perceived Type for the extension.
A perceived type is a category of file types that lets you identify your file type to Windows (and applications) as being an image, audio, document, or other type. Perceived types are used for several purposes, including the determination of the folder type, which is then used to set the default view settings. For example, a folder full of files that are of the perceived type image is assigned a default view mode of thumbnails.
This will allow you to change the Content Type for the extension