Associate a File Type with a Specific Program
How do I change file association via the cmd.exe prompt?
I know this is similar to this question, but I'm only concerned with CMD.
I'm editing my answer, because you can do it. The FTYPE command, in conjunction with the ASSOC command will let you change file associations.
To find your file type associations, you use the assoc command at the command prompt. Make sure you pipe it to the more filter because the list is quite long and will scroll out of your buffer.
After you know how you want to change the file associations, use the ftype command: