personalized octopus card as a souvenir

how many days can i get the personalized octopus card?we will stay in hongkong only for 3 days and iwant to have a personalized octopus card to use during my stay in 3 days .can i keep the personalized octopus card as my souvenir but i want to refund the remaining balance if thers any and keep the card assouvenir?