How do you track whether a rebrand actually changed how people feel about a product?

The cleanest approach I've seen is a pre/post brand perception tracker using the same 5-6 attribute scales (modern, trustworthy, premium, etc.) so you have a direct apples-to-apples comparison. If you didn't run a pre-wave before launch, you can still do a monadic split test now — show half your sample the old pack and half the new one and compare scores. Tools like Momentive or even a quick Qualtrics survey with 200-300 category buyers will get you there fast.