New Coke, New Ingredients
When Coca-Cola introduced New Coke, the reception was underwhelming at best. In fact, most people were convinced that the best thing the company could do was return to their original recipe. Eventually, that is what happened. But this conspiracy suggests that the transition back to regular coke was just a way to introduce a new ingredient.
The theory is that all the controversy about New Coke was a convenient way for Coca-Cola to begin adding high fructose corn syrup to their drinks. With all the discussion and dislike towards New Coke, adding high fructose corn syrup without anyone noticing would not be that hard to do. However, they would have probably started using it no matter what.