For the black-bean topping variation, top the potatoes with the yogurt and scallions after removing them from the oven. The sour-cream version requires no reheating whatsoever.
Preheat oven to 400 degrees with rack in center. Prick potatoes all over with a fork and rub with oil. Place on rack and bake until potatoes are easily pierced with the tip of a sharp knife, about 1 hour. Remove from oven and transfer to a parchment-lined baking sheet.
Split potatoes, pressing ends to create a pocket in each. Add a dab of butter or drizzle with oil; season with salt and pepper. Stuff with desired toppings; return to oven to warm through, if needed (see note, above), about 5 minutes, before serving.