Custom commerce order_id
You cannot change order id as other functionalities are dependent on it.But you can change order number before saving order to shopping cart status by using  hook_commerce_order_presave($order).

function example_commerce_order_presave($order) {
   if ($order-&gt;status == 'cart') {
   $order-&gt;order_number = 'new order number;
   commerce_order_save($order);
   }
 }