using wp_update_post on save_post

The reason it’s going to be infinite is that every time you save the post, it’s calling change_year…which then calls wp_update_post … which fires the save_post filter.

After some review and research, I’m thinking that you should probably avoid the save_post filter.

Try using this filter:
http://codex.wordpress.org/Plugin_API/Filter_Reference/wp_insert_post_data

It gives you really what you want.

Here’s an example of it editing posted data:

function filter_handler( $data , $postarr ) {
    $data[ 'post_title' ] = $postarr[ 'post_title' ] . 'RAWR!';
    return $data;
}
add_filter( 'wp_insert_post_data' , 'filter_handler' , '99', 2 );

That will take any post that I save and add ‘RAWR!’ to the end of the string.

Hope this helps.