How can I alter a plugin's function from my theme's functions.php?

The code below is from the "All in One SEO" pack plugin. It alters my theme's 404 page title. I understand that's how this particular plugin works, however, in this instance, its conflicting with my theme's onboard management of 404 post titles and I need to override it.

My question is, from my functions.php file, how can I intercerpt and nullify the is_404() code brance in the code below?

class All_in_One_SEO_Pack {

function rewrite_title($header) {
    global $aioseop_options;
    global $wp_query;
    if (!$wp_query) {
        $header .= "<!-- no wp_query found! -->\n";
        return $header; 
    }

    $post = $wp_query->get_queried_object();

    // the_search_query() is not suitable, it cannot just return
    global $s;

    global $STagging;

    if (is_home() && !$this->is_static_posts_page()) {
        $title = $this->internationalize($aioseop_options['aiosp_home_title']);
        if (empty($title)) {
            $title = $this->internationalize(get_option('blogname'));
        }
        $title = $this->paged_title($title);
        $header = $this->replace_title($header, $title);
    } else if (is_attachment()) { 
                        $title = get_the_title($post->post_parent).' '.$post->post_title.' – '.get_option('blogname');
                        $header = $this->replace_title($header,$title);
    } else if (is_single()) {
        // we're not in the loop :(
        $authordata = get_userdata($post->post_author);
        $categories = get_the_category();
        $category = '';
        if (count($categories) > 0) {
            $category = $categories[0]->cat_name;
        }
        $title = $this->internationalize(get_post_meta($post->ID, "_aioseop_title", true));
        if (!$title) {
            $title = $this->internationali开发者_如何学Pythonze(get_post_meta($post->ID, "title_tag", true));
            if (!$title) {
                $title = $this->internationalize(wp_title('', false));
            }
        }
        $title_format = $aioseop_options['aiosp_post_title_format'];
        /*
        $new_title = str_replace('%blog_title%', $this->internationalize(get_bloginfo('name')), $title_format);
        $new_title = str_replace('%blog_description%', $this->internationalize(get_bloginfo('description')), $new_title);
        $new_title = str_replace('%post_title%', $title, $new_title);
        $new_title = str_replace('%category%', $category, $new_title);
        $new_title = str_replace('%category_title%', $category, $new_title);
        $new_title = str_replace('%post_author_login%', $authordata->user_login, $new_title);
        $new_title = str_replace('%post_author_nicename%', $authordata->user_nicename, $new_title);
        $new_title = str_replace('%post_author_firstname%', ucwords($authordata->first_name), $new_title);
        $new_title = str_replace('%post_author_lastname%', ucwords($authordata->last_name), $new_title);
        */
        $r_title = array('%blog_title%','%blog_description%','%post_title%','%category%','%category_title%','%post_author_login%','%post_author_nicename%','%post_author_firstname%','%post_author_lastname%');
        $d_title = array($this->internationalize(get_bloginfo('name')),$this->internationalize(get_bloginfo('description')),$title, $category, $category, $authordata->user_login, $authordata->user_nicename, ucwords($authordata->first_name), ucwords($authordata->last_name));
        $title = trim(str_replace($r_title, $d_title, $title_format));

        $title = apply_filters('aioseop_title_single',$title);
        $header = $this->replace_title($header, $title);
    } else if (is_search() && isset($s) && !empty($s)) {
        if (function_exists('attribute_escape')) {
            $search = attribute_escape(stripcslashes($s));
        } else {
            $search = wp_specialchars(stripcslashes($s), true);
        }
        $search = $this->capitalize($search);
        $title_format = $aioseop_options['aiosp_search_title_format'];
        $title = str_replace('%blog_title%', $this->internationalize(get_bloginfo('name')), $title_format);
        $title = str_replace('%blog_description%', $this->internationalize(get_bloginfo('description')), $title);
        $title = str_replace('%search%', $search, $title);
        $header = $this->replace_title($header, $title);
    } else if (is_category() && !is_feed()) {
        $category_description = $this->internationalize(category_description());
            if($aioseop_options['aiosp_cap_cats']){
                $category_name = ucwords($this->internationalize(single_cat_title('', false)));
            }else{
                    $category_name = $this->internationalize(single_cat_title('', false));
            }           
        //$category_name = ucwords($this->internationalize(single_cat_title('', false)));
        $title_format = $aioseop_options['aiosp_category_title_format'];
        $title = str_replace('%category_title%', $category_name, $title_format);
        $title = str_replace('%category_description%', $category_description, $title);
        $title = str_replace('%blog_title%', $this->internationalize(get_bloginfo('name')), $title);
        $title = str_replace('%blog_description%', $this->internationalize(get_bloginfo('description')), $title);
        $title = $this->paged_title($title);
        $header = $this->replace_title($header, $title);
    } else if (is_page() || $this->is_static_posts_page()) {
        // we're not in the loop :(
        $authordata = get_userdata($post->post_author);
        if ($this->is_static_front_page()) {
            if ($this->internationalize($aioseop_options['aiosp_home_title'])) {

                        //home title filter
                        $home_title = $this->internationalize($aioseop_options['aiosp_home_title']);
                        $home_title = apply_filters('aioseop_home_page_title',$home_title);
                        $header = $this->replace_title($header, $home_title);

            }
        } else {
            $title = $this->internationalize(get_post_meta($post->ID, "_aioseop_title", true));
            if (!$title) {
                $title = $this->internationalize(wp_title('', false));
            }
            $title_format = $aioseop_options['aiosp_page_title_format'];
            $new_title = str_replace('%blog_title%', $this->internationalize(get_bloginfo('name')), $title_format);
            $new_title = str_replace('%blog_description%', $this->internationalize(get_bloginfo('description')), $new_title);
            $new_title = str_replace('%page_title%', $title, $new_title);
            $new_title = str_replace('%page_author_login%', $authordata->user_login, $new_title);
            $new_title = str_replace('%page_author_nicename%', $authordata->user_nicename, $new_title);
            $new_title = str_replace('%page_author_firstname%', ucwords($authordata->first_name), $new_title);
            $new_title = str_replace('%page_author_lastname%', ucwords($authordata->last_name), $new_title);
            $title = trim($new_title);
                            $title = $this->paged_title($title);
            $title = apply_filters('aioseop_title_page',$title);
            $header = $this->replace_title($header, $title);
        }
    } else if (function_exists('is_tag') && is_tag()) {
        global $utw;
        if ($utw) {
            $tags = $utw->GetCurrentTagSet();
            $tag = $tags[0]->tag;
            $tag = str_replace('-', ' ', $tag);
        } else {
            // wordpress > 2.3
            $tag = $this->internationalize(wp_title('', false));
        }
        if ($tag) {
            $tag = $this->capitalize($tag);
            $title_format = $aioseop_options['aiosp_tag_title_format'];
            $title = str_replace('%blog_title%', $this->internationalize(get_bloginfo('name')), $title_format);
            $title = str_replace('%blog_description%', $this->internationalize(get_bloginfo('description')), $title);
            $title = str_replace('%tag%', $tag, $title);
            $title = $this->paged_title($title);
            $header = $this->replace_title($header, $title);
    } else if (is_404()) {
        $title_format = $aioseop_options['aiosp_404_title_format'];
        $new_title = str_replace('%blog_title%', $this->internationalize(get_bloginfo('name')), $title_format);
        $new_title = str_replace('%blog_description%', $this->internationalize(get_bloginfo('description')), $new_title);
        $new_title = str_replace('%request_url%', $_SERVER['REQUEST_URI'], $new_title);
        $new_title = str_replace('%request_words%', $this->request_as_words($_SERVER['REQUEST_URI']), $new_title);
        $new_title = str_replace('%404_title%', $this->internationalize(wp_title('', false)), $new_title);
        $header = $this->replace_title($header, $new_title);
    }

    return $header;

}}

I don't know if template tags work in non-template files, but if they do, and you don't mind altering the plugin code, you can attempt your interception of the plugin's code by creating and adding your own action hook.

This is just about the same as modifying the plugin code in place, except your custom code is placed in your own plugin or functions.php.

If you are unfamiliar with custom action hooks, here's an article that describes the process: http://archive.extralogical.net/2007/06/wphooks/