Good planning,butts can be an interesting experience when shooting for a time! I would reheat in the oven at 350 tightly foiled maybe add some finishing sauce to keep it extra moist and flavorful,or a bbq sauce of your choosing, I put sauce only on top of a Sammie generally. You can find various finishing sauces using the search feature. I would fully cook and rest the butt pull it and just cover tightly or store it in a ziplock bag. The best way I can think of to cool the meat after pulling is to spread it out on a sheet pan and stick it in your fridge or freezer for a bit to get it chilled and out of the danger zone faster. You want to reheat the pork to 160 when I reheat in the oven I cover the dish with plastic wrap then foil it seems to help seal the moisture in as well as the steam doesn't escape.