Sure.

Please note that with the mobile pass you can choose the starting date after purchase. For the Paper Paper at the purchase because it will be printed on the Ticket. 

This is technically possible, but you would be missing out on travel days. If your travel plans have changed, you can reach out to our customer service team to request an exchange so that you can choose a different start date (please note that this will not be possible for certain promotional passes). If you have a mobile pass, you can simply de-activate the pass before the pass is due to start and select a new start date.