First, let me say I have no idea why you'd want to do that.
Second, let me say it's almost certainly possible since the video player is a modified mplayer, which supports that. Hell, they probably left the "view as ASCII art" option in. However, you'd need command-line access to do it.
Or you could write a script, though it would be set to run a specific file, unless you worked with the selector... I'm not to clear on how to use that, though.
Does some enterprising lad want to see what mplayer features the GP2X has in it? Because I certainly don't really care enough to bother (though it might be nice to change the saturation at times).