I have "roasted" peanuts ( and other nuts) in a frying pan on a burner. Watch them closely and stir often , it produces good flavor. Adding oil is optional. They were used immediately so I don't know about shelf life.
You can, just like you would for raw peanuts. However the boiled/poached peanuts have a bitter taste that is not removed by roasting and is generally unpleasant to eat as a snack. I would use these peanuts to make peanut sauces such as satay sauce, and possibly in other dishes where the peanuts are not the dominant flavor.