Yes, beef rendang can be frozen and reheated. In fact, I think that rendang tastes even better after the flavors have had time to meld together. Like all stews, this just gets better when it sits a couple of days in the fridge. Allow the dish to cool completely before storing it in an airtight container in the freezer. When reheating, gently warm it on the stovetop, adding a little water or coconut milk if needed to prevent it from drying out completely.