bulk post_content update

This is what I mean:

<?php 
$tochange = get_posts('numberposts=-1&post_type=any&category_name=category-name-you-want-to-change');
foreach($tochange as $post){
    setup_postdata($post);
        $contentchange=""; /*here you do the magic, string replace or whathever you want to do*/
        $tochange = array();
        $tochange['ID'] = $post->ID;
        $tochange['post_content'] = $contentchange;
        $out = wp_update_post($tochange);
        unset($tochange);
    }
wp_reset_query();
?>