<div class="big_content_item">CONTENT</div>

<div class="wide_content_item">CONTENT</div>

<div class="content_item">CONTENT</div>

[big_content] или [wide_content] или [content]

add_filter('the_content', 'filter_content');
function filter_content( $content ){
    modify_content($content, '[big_content]', '<div class="big_content_item"';
    modify_content($content, '[wide_content]', '<div class="wide_content_item"');
    modify_content($content, '[content]', '<div class="content_content_item"');
    return $content;
}
function modify_content($content, $code, $wrap) {
    if (substr($content, $code) {
        $content = str_replace($code, '');
        return $wrap . $content . '</div>';
    }
}