Открываем engine/modules/show.full.php
Находим:
$db->query( "SELECT id, title, date, category, alt_name, flag FROM " . PREFIX . "_post WHERE MATCH (title, short_story, full_story, xfields) AGAINST ('$body') AND id != " . $row['id'] . " AND approve='1'" . $where_date . " LIMIT " . $config['related_number'] );
Меняем на:
$db->query( "SELECT id, title, date, category, alt_name, flag FROM " . PREFIX . "_post WHERE MATCH (title, short_story, full_story, xfields) AGAINST ('$body') AND id != " . $row['id'] . " AND approve='1' AND category regexp '[[:<:]](1|2|3)[[:>:]]'" . $where_date . " LIMIT " . $config['related_number'] );
Где 1|2|3 — нужные категории.
