Hello,
With time and development, everything is possible.
In your case, it would require to change how the vendor selector custom field is acting in order to be able to filter the vendors you want to display into. It might require to interact with the namebox system and also add some verification for the vendor assignation to be sure that the customer did not select a value which won't be authorized.
It is some development, it need some PHP en coding skills but it is not a huge or impossible development.
The namebox part is currently the most difficult one to estimate since it could need some tests to choose the best implementation.
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.