custom post info for a specific category

[pxforti]

Template: Enterprise; wp 3.3.2

I want to customize post info for a specific category and leave all other posts with the default post info.

I'm using the following code in my child functions.php, but it removes post info for all other posts.

PHP Code:

/** Customize the post info function */
add_filter( 'genesis_post_info', 'post_info_filter' );
function post_info_filter($post_info) {
if (!is_page() && in_category(4)) {
    $post_info = '[post_date]';
   return $post_info;
    }
} 


Is there a way to apply this to a specific category but leave all other posts with the default post info?

Thanks