I don't know.... I know that consumer protection is pretty much non-existent in US but a price of a product is still a price of a product. Let's say they want to go all-in, ignore the law and just charge everyone whatever they want. They would simply put a price 10% below real price on every sticker and charge you something else at the register. They would say that the price on the sticker is approximate and you have to identify yourself to know the real price. After scanning your consumer cart or your credit card they would show you the final amount. It would be way simpler than to put digital stickers, track the movement of every customer in real time, use face recognition to identify them and adjust the prices close to them. Technically they could do all this but for what? Why develop some hi-tech solution when a simpler solution is equally illegal? People would be pissed either way so they will do it only if they know their customers have nowhere else to go. I don't see any reason to play a game like that. Occam's razor: they want to change prices at night.

P.S. Unless they want to change the price for everyone in the middle of the day and the stickers are there so only first 20 customers are surprised at the register and start complaining. The rest picked up the product with the new price already... This makes some sense but it would be done in rare cases like unexpected weather change so they increase the price on umbrellas or something. But yeah, I could see that happening.