I am afraid i don't have any solution that i can provide you about this.
I never interested in Hacking Virtuemart (modifying virtuemart core files)
You can do this: (without needing any core hack)
Lets say you have this category tree:
Laptop
- Acer
- Asus
- HP
And once you create a product for HP, choose "Laptop" and "HP" as categories. So the same product will be visible in both Laptop and HP categories.
This is the most appropriate way to do it; but i know, it will be lots of time consuming if you have too many products.
Topic is closed for forum clearance.
Regards.
Forum Support.