Hi,
When you change the status of an order in the backend, the email that you would send is generated before that the status is changed.
We can assign serials before because, when you would click on "ok", the status would change and the email would be sent. If you close the window, nothing would change so, if the serials were assigned, there would be a error.
I think we would add a little button near the order status dropdown, this button would open the popup, like the dropdown but would not change the status of the order, just to "re-sent" an email.
After that, you can change the status of the order to "shipped" (and do not notify the customer) and then change to "confirmed" (and notify the customer).
Serials would be assigned during "shipped" modification, so there would be present in the "confirmation email".
If you don't want to use the "shipped" status, you can create a "pre-confirmed" status (or other name) which would be configured in HikaSerial as "Assignable order status".
This transitional status would help you to generate and assign serials before the confirmation and the confirmation email.
Regards,