Days following Coolsculpting procedure to upper and lower abs -how to optimize/not sabotage results?

Your overeating should not affect the procedure.  I would try your best to maintain a healthy diet and try to exercise.  Theoretically, the coolsculpting treatment will reduce the number of fat cells in the area treated so you may not gain as much fat in the treated area in the future, if you gain weight.

The best way to optimize your CoolSculpting results is to maintain a healthy diet and exercise. A few heavy meals won't have a negative effect in the long run, but gaining significant weight because of a poor diet and lack of physical activity will not give you the best possible results. Remember, the fat cells that get frozen by CoolSculpting will not return, but the remaining fat cells in the area can always increase in size and mask your results.

Overeating for a day or so after a CoolSculpting treatment should not affect your results.  If you were overeating consistently over a longer period of time, then you most likely would not see optimal results.  The fat cell death that occurs after CoolSculpting would not be affected by the diet, but the existing fat cells that were not killed off could enlarge if someone ate excessively.