Can you use greedy dice if your prize cards are face up?

Are you allowed to play greedy dice/use Jirachi prism"s ability if your prizes are face up? Like if you played a town map or a here comes team rocket, which both turn your prize cards face up. Greedy dice/Jirachi prism's ability both say to do something with your face down prize cards, but I was wondering if that is a requirement, or just a bit of flavor text.