For someone who eats a fat based, low-moderate carb diet, 2-3 days of high carbs will greatly decrease the amount of insulin needed for cells to take up carbs, and also will increase glucose burning enzyme concentrations and lead to increase glycogen storage. It is important to know that this has to be done with low fat consumption. The lowish carb dieter (20%-30%) has their muscles primarily loaded with fatty acids and with enzymes to process fatty acids, and does not store as much glycogen or use glycogen as readily for work.
It only takes about 3 days to drastically increase cells ability to take up and use glucose.
My son is type 1 diabetic and usually eats around 25% carbs, 60% fat, but if he eats low fat and high carbs for 3 days the amount of insulin he needs for a given amount of carbs is cut in half or less. (he will typically go from about 8 grams of carbs covered by a unit of insulin to 15-20, but of course he is consuming 2.5x as many carbs, so an interesting discovery we have made (and is also being seen in other research) is that insulin needs are practically independent on the breakdown of carbs and fat in the diet, given the same number of calories. Low carb, high fat diets don't reduce total daily insulin exposure very much, they just reduce peak levels, peak blood sugars, and also reduce low blood sugar 2-4 hours after a meal which are common with high carbs.
Anyway, for a low carb eater to have 48-96 hours of high carbs and low fat definitely increases the body's ability to use glucose for fuel and builds glycogen reserves. After long though the ability to burn fat diminishes to match. Also it only takes a couple of days of high fat to go back to being a less efficient carb processor.
I will try to post more in a bit.