As Billy said, it wont stay crispy after it is cooled. However that is perfectly fine! 95% of the pork belly you buy in restaurants is prepared that way. Simply cook the pork belly as desired (braise, roast, sous vide etc..) and then chill/refrigerate. Once cooled, cut your belly into the desired serving size. To reheat/crisp, you'll want to sear/brown the pieces in a skillet/pan/flat top etc.. if the portion sizes are larger, you can finish them in the oven after the sear/browning step.