Hi,
When we built HikaMarket 1.0.0, we imagine this way of registration but we didn't know if it was good to have one single key for a vendor.
That's why we just put the addition of manager by the vendor administrator and we did not put this specific feature.
But in the way you describe it, where the key will be unique for a specific user and only send when the manager try to add an email, I think it is a good approach !
So I will put your request in the HikaMarket TODO list.
I don't know when I will start to work on it, we just release HikaMarket 1.4.0 so I just start to work on the product characteristic edition in the front-end !
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.