Why would you ever need to duplicate an order in Magento? A few weeks ago I would have asked the same question. In this instance, it was caused by needed to re-send a subscription order through to an ERP after the expiration window for the order had expired at the payment provider. This script duplicates the order and assigns it a new increment ID. It does not re-authorize the card or do any other financial transactions.
Github: https://github.com/seanbreeden/magento-duplicate-order.git
Usage:
php duplicate_order.php <original_increment_id>