I cooked a kilo pork belly yesterday with a very nice crackling in a roasting pan with a rack so that the pork does not touch the pan. Once we had dinner, I put it in the fridge without covering (in the same tray with the rack I roasted it).
I have reheated pork belly in the past in a microwave but that just makes the crackling chewy. Is it possible to reheat pork belly without losing the crackling or over-drying the meat?
Try reheating it in the oven or a toaster oven; the dry heat should prevent things from getting chewy. The microwave often imparts undesirable texture changes in food when it heats things, so that's probably your issue more than the refrigeration; any condensation from the fridge should evaporate when exposed to dry heat. I'd toss it in at 350 and check on it periodically until it's warmed enough for you.
The reason why your pork crackling became soft after taking out of fridge is because the skin crackling process wasn't 100% complete. A perfect crackling stays crisp even after 2 days sitting in the fridge.
Having said that. The simplest reheat process is to place the entire piece of meat with skin facing up in an air fryer or conventional over ( never use the microwave ). Reheat at 400F for 10-15 minutes.
To prevent the softer meat from burning, wrap aluminium foil around it.
I like the air fryer approach. I reheated at 400 degrees for 9 minutes since the skin was originally properly cooked. I placed the belly on the side of the rack to keep it upright with the skin up. The skin is crunchy, the meat moist and my tongue/stomach are happy.