We will create the User and password for our members and email them - just like a coupon
The only different is that I want to update the database with the new user info (login and password)
Scenario
1 - Visitor fill up a short form including his email address.
2 - Hika sends him email with login and password
We are all happy
HikaSerial does not have a user generator and even if it has one, there is no feature which will feet to your requirement for creating some kind of "trigger" when a customer enter his username.
I think it will be easier to implement is as a custom development (with a custom module and a custom plugin).
Regards,