Инструкция:
в файле ./engine/inc/search.php найти:
        if (in_array(\"news\", $_POST[\'table\'])) {
                $db->query(\"UPDATE `\" . PREFIX . \"_post` SET `short_story`=REPLACE(`short_story`,\'$find\',\'$replace\')
\");
                $db->query(\"UPDATE `\" . PREFIX . \"_post` SET `full_story`=REPLACE(`full_story`,\'$find\',\'$replace\')
\");
                $db->query(\"UPDATE `\" . PREFIX . \"_post` SET `xfields`=REPLACE(`xfields`,\'$find\',\'$replace\')\"
);

        }

        if (in_array(\"comments\", $_POST[\'table\'])) {
                $db->query(\"UPDATE `\" . PREFIX . \"_comments` SET `text`=REPLACE(`text`,\'$find\',\'$replace\')\")
;
        }

        if (in_array(\"pm\", $_POST[\'table\'])) {
                $db->query(\"UPDATE `\" . USERPREFIX . \"_pm` SET `text`=REPLACE(`text`,\'$find\',\'$replace\')\")
;
        }

        if (in_array(\"static\", $_POST[\'table\'])) {
                $db->query(\"UPDATE `\" . PREFIX . \"_static` SET `template`=REPLACE(`template`,\'$find\',\'$replace\')\"
);

        }

        if (in_array(\"tags\", $_POST[\'table\'])) {
                $db->query(\"UPDATE `\" . PREFIX . \"_tags` SET `tag`=REPLACE(`tag`,\'$find\',\'$replace\')\");
                $db->query(\"UPDATE `\" . PREFIX . \"_post` SET `tags`=REPLACE(`tags`,\'$find\',\'$replace\')\")
;
         }

        clear_cache ();
        msg(\"info\", $lang[\'find_done_h\'], $lang[\'find_done\'], \"?mod=search\");

}

и заменить на:
        foreach ( $_POST[\'table\'] as $value ) {
        
                if ($value == \"comments\") {
                        $db->query(\"UPDATE `\" . PREFIX . \"_comments` SET `text`=REPLACE(`text`,\'$find\',\'$replace\')\")
;
                }
        
                elseif ($value == \"pm\") {
                        $db->query(\"UPDATE `\" . USERPREFIX . \"_pm` SET `text`=REPLACE(`text`,\'$find\',\'$replace\')\")
;
                }
        
                elseif ($value == \"static\") {
                        $db->query(\"UPDATE `\" . PREFIX . \"_static` SET `template`=REPLACE(`template`,\'$find\',\'$replace\')\"
);
                }
        
                elseif ($value == \"tags\") {
                        $db->query(\"UPDATE `\" . PREFIX . \"_tags` SET `tag`=REPLACE(`tag`,\'$find\',\'$replace\')\");
                        $db->query(\"UPDATE `\" . PREFIX . \"_post` SET `tags`=REPLACE(`tags`,\'$find\',\'$replace\')\")
;
                }

                else {
                        if ($config[\'allow_multi_category\'])
                                $where_category = \"category regexp \'[[:<:]](\" . $value . \")[[:>:]]\'\";
                        else
                                $where_category = \"category = \'{$value}\'\";
        
                        $db->query(\"UPDATE `\" . PREFIX . \"_post` SET `short_story`=REPLACE(`short_story`,\'$find\',\'$replace\')
WHERE {$where_category};\");
                        $db->query(\"UPDATE `\" . PREFIX . \"_post` SET `full_story`=REPLACE(`full_story`,\'$find\',\'$replace\')
WHERE {$where_category};\");
                        $db->query(\"UPDATE `\" . PREFIX . \"_post` SET `xfields`=REPLACE(`xfields`,\'$find\',\'$replace\') WHERE {$where_category};\");
                }
        }

        clear_cache ();
        msg(\"info\", $lang[\'find_done_h\'], $lang[\'find_done\'], \"?mod=search\");

}

        $categoryes = array ();
        $db->query ( \"SELECT id, name FROM \" . PREFIX . \"_category ORDER BY posi ASC\" );
        while ( $row = $db->get_row () ) {
                $categoryes_option .= \'<option value=\"\'.$row[\'id\'].\'\" selected>-- \'.$row[\'name\'].\'</option>\';
        }
        $db->free ();

найти:
<option value=\"news\" selected>{$lang[\'find_rnews\']}</option>

заменить на:
<optgroup label=\"{$lang[\'find_rnews\']}\">{$categoryes_option}</optgroup>

КСТАТИ, для удобства: в этом же файле найти:
<select name=\"table[]\" style=\"height:72px;\" multiple>

заменить на:
<select name=\"table[]\" style=\"height:272px;\" multiple>

Вот и все.
Актуально для DLE 6.5 - DLE 8.3