It doesn't matter which magnetic strip card you use. You are not suppose to use the same one for the cabin door though.
If you lose your credit card to open the safe, the purser's desk will send someone up to your cabin to open the safe and the you just have to use a different card. You can change cards each time you lock the safe.
(cruzin' solo by design)
Freedom ('09), Imagination ('08), Victory ('08), Destiny ('08), RCCL Navigator ('08), RCCL Majesty ('08), Glory ('07), Liberty ('07), Fantasy ('07), Destiny ('06), NCL PofAm ('05), Fascination ('04), Victory ('04), Fascination ('04), RCCL Voyager ('03), Fantasy ('99)