“This is like the largest blind tasting ever”
Insight: Brand is all about perception. When you are changing the recipe of an iconic food item, you have to be careful. Expectations play important role on what we taste and how we experience it. Taste is shaped by our past experiences, our current mood, our expectations, and any number of incidental details.
“What we think is going into our mouth actually changes what we taste, down to the level of the taste buds themselves.”
– Michael Norton, assistant professor of business administration in the marketing department of the Harvard Business School
So instead of doing big bang like New Coke and failing miserably, Mac & Cheese starts sneakily by just testing it out. Not surprisingly people didn´t notice any difference and generally having no artificial ingredients should be good thing. 
I also recommend watching this longer story about the project and to visit the website.
Powerful, simple, big and real (not scam or some crappy innovation) campaigns are not that common nowadays, so this definitely deserves some praise.
Stand-Up Strategy 