Hi,
The "series" generator is like a counter increment generator.
It uses the other serials in order to get the current counter value (the highest value for the current pack).
You can access to all product fields in the "generate" function, so you can read a custom field of a product.
But you would have to edit the value of the product custom field with a SQL query afterwards.
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.