Hi,
For the moment in order to override the email, the best is to use the HikaShop mail triggers.
Thanks to that trigger, you can modify the email destination emails.
But I have added a new trigger for the next HikaSerial release so it would be possible to be "triggered" when a pack stock quantity is being low.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.