You can add days to any ticket. All you will pay is the difference between the price of the number of days on the current ticket and the price for the number of days on the new tickets.
The following rules apply:
1. No ticket (other than an annual pass) may have more than ten days of entry on it, counting both used and unused.
2. A ticket is valid for 14 days from first use. If day one is a Sunday, day 14 is the second Saturday following.
3. Any upgrade must be done prior to the close of business on the day that you have used your last entry, even if less than 14 days. (This does not apply if you have a room plus tickets package and are staying at a Disney Resort.)