Custom file extensions for windows video file

Hello all,

Is it possible to programmatically change the file extension for a
windows video file (*.wma/*.wmv) to an entirely different extension,
for e.g., *.abc ? How can I do it in vb.net?
I am actually encoding a screen capture into a .wmv file and playing it
in WMP.
I was able to change the extension manually from a .wmv to a .abc and
play it in WMP in spite of WMP displaying an error message saying "The
selected file has an extension that is not recognised by Windows Media
Player, but the Player may still be able to play it....."
How damaging can it be?

Thanks for your help.
TS