Trying to overwrite category through filter

I understand Postie has the ‘starts with logic’ but I’m trying to make it more robust for my case by using a PHP switch case to set the category based on a specified words found in the subject line. And so $new_category would be assigned to $post[‘post_category’].

Before even inserting the switch, I just tried overwriting the post’s category using $post[‘post_category’] = 44; and $post[‘post_category’] = ‘news’; but neither worked (‘news’ is an existing category). Instead, the posts just got assigned the default “General” category.

filterPostie.php:

add_filter('postie_post_before', 'filter_customized');

function filter_customized($post) {
        
        $post['post_title'] = 'News Update';  //this works just an example
        
        $post['post_category'] = 44;
        // neither of these work
        $post['post_category'] = 'news';

        return $post;
}

Thank you.