So they can add a day prior to using them at a park?
I think I'm confusing myself now.
Disney tickets are very confusing. If you have tickets that you bought from Disney Online, and you haven't arrived for your trip yet, you can't change them to add days. You can only buy more tickets. This is usually an expensive idea, except for adding a single day ticket for day 2 or a single day ticket for day 3. Otherwise one should wait to arrive at WDW and do an upgrade.
When you arrive in WDW with your tickets, and want to add days, you can do that inside or outside a theme park.
Some tickets, like old resort package tickets, if they are worth less than gate price, they can be used to enter a theme park, and that will bring them up to current price.
Other tickets, like Disney Online tickets, if they are worth less than gate price, entering a theme park
will not bring them up to current gate price. As I said to last poster, their tickets were from Disney Online, so they might as well upgrade them outside a park gate because it wouldn't change how much they were worth. The same goes for your tickets, too, from Disney Online.