Rebranding is the process by which a product or service developed with one brand, company or product line affiliation is marketed or distributed with a different identity.
http://en.wikipedia.org/wiki/Rebranding

If the product changes for example die-shrink or hardware based for example DX11 then it can't be called rebranding. Rebranding is the exact same product with a different identity or name.

I don't agree how Nvidia plays the game with its Geforce, like saaya already said AMD has been doing a better job with its Radeon.