One product multiple brands

I need to assign multiple brands/manufacturers for certain products. Is it doable?

As far as I know, no, out of the box it's not doable, and as far as I can see, it would require major code changes to make it doable.
Well, then you have to admit that it's a extremely unusual need.

But since you're using a commercial HikaShop version, why don't you use a custom field for brands instead of the core manufacturer feature?

P.S.: Are you using a very old HikaShop version, or why are you posting in the "Archives" section?