Answer:
To Create a New File Extension File Association or Edit a currently existing one:
1. Open any Folder (e.g. My Documents or a random folder)
2. Click on Tools then Folder Options
3. Click on the File Types tab
A. To Create a New File Extension Click New
B. Enter the new file extension Then click Advanced and select the program to open the type of file with.
A. To Edit a File Extension Click on the File you want to change in the scroll list.
B. Click Edit and change settings to your wanted option.
Hope this Helped :D