Well I did this myself but only wet it, as I didn't want to mess that much. It felt like the wetness didn't go away that easily and when I was done I developed a rash. So keep that in mind. Diapers keep the wetness away from your skin, as they were designed to. If you're going to mess in your underwear with a diaper over them, I guess it'll be the same as messing as regular only you'll have the diaper over so you won't have to worry about containing the mess.