How to Change a File Association With Group Policy
Group policies are a part of a Windows domain that controls the desktop interface on users' client machines. The policies control the applications a user can load, Internet browsing, drive mapping and even file associations. The group policy is edited on the main Windows server by a network administrator. The file association policy forces an application to load when a user double-clicks a file with a certain extension.
Click the Windows server "Start" button and then click "Administrative Tools." Click "Group Policy Management Console" to open the policy manager.
Right-click the group policy server name and select "Edit." In the list of options, click "Computer Configuration," "Preferences," then "Control Panel Settings."
Right-click the "Folder Options" icon and select "New," then "File Type." This opens a new configuration window.
Select "Create" from the "Actions" drop-down box. Select "File Extension" from the "File Type Settings" drop-down box.
Enter the file extension for the new group policy. Select a program from the list of software in the "Association" list. Click "OK" to save your settings and close the group policy editor.