using the filter 'upload_dir'

I want to override the /year/month scheme and upload my files to a specific folder. I've copied the following code form codex.wordpress and inserted in my theme functions.php:

add_filter('upload_dir', 'awesome_wallpaper_dir');

function awesome_wallpaper_dir( $param ){
   $mydir = '/awesome';

   $param['path'] = $param['path'] . $mydir;
   $param['url'] = $param['url'] . $mydir;

   return $param;
}

but when I upload a file it is stored in /year/month subdir. What's wrong?