If you purchase tickets for a certain day, but are unable to go, can you use them a different day?

Same day tickets only

Just a note. Pay what you want tickets are only for new york citizens. Ask if you have already purchased. The customer service there are very nice and accommodating.

No, they accept only same day tickets. An alternative to buying tickets would be to buy 'Pay what you want' tickets on the day.

Same day only, the date is printed on the ticket. You may be able to ask the front desks for an exchange.