If you are on a low carb diet, then read the paleo diet for athletes. It explains how to time carbs, and what types around your riding. I also eat low carb, but the night before a long/high intensity ride I will eat a sweet potato. If carbs aren't bad for you in general, then your plan to just eat a more balanced diet the week before the event is good.

But I can ride a century on low carb, since I use low carb to control mild type I diabetes, but to do it you need to train yourself to burn a higher ratio of fat to carbs, ride at moderate not high intensities, and drink a protein drink with electrolytes (Jay Robb) on the bike so u can fuel your rides with the by products of amino acid metabolism (you can deaminate amino acids to carbon skeletons which feed into the TCA cycle). But this is a way of life for me, not something I would do on a single ride, or attempt to do for the first time, on a long event ride.