If it is a whole butt, not pulled, you can reheat in the foil. Just make sure it is thawed all the way through. It will take a few days in the fridge. If the butt was done when you took it off the smoker, you just need to heat to 160*F. You wil know if you need to heat it more by how it pulls. I reheat whole butts/shoulders at the restaraunt every day.
Team: Pyle's BBQ; Yoder YS640; Good-One "Trail Boss" 60T; Weber Kettle w/rotisserie ring; Big A$$ Rotisserie; Weber OTS; New Braunfels offset smoker.
Saddles BBQ Bistro