adding a day to a ticket not originally purchased through Disney?

[O'MalleytheAlleyCat]

I purchased tickets for some guests that we're taking on vacation with us next week through a non-Disney seller. They are 4 day hopper tickets and we've already linked them to our Magic Bands. We think we may want to add one extra day to those tickets once we get to the parks. I know we only have to pay the difference between a 4 day ticket and a 5 day ticket to add the extra day. Would that amount be based on what the tickets cost if purchased through Disney? If I look at the website correctly, I think that would be about $6.50 per ticket. Even though Disney is currently offering a 4 day ticket with the 5th day free, I assume we'd still have to pay the difference between the 4 day ticket and the 5 day ticket. Does all this sound correct?

[VWL Mom]

It used to be that if you bought a ticket from a broker you would use one day and then upgrade and would receive the full Disney value on the brokers ticket. Since the increase in February they are saying that they will track the original price whether you use it or not and you will first pay the difference in price and then the upgrade fee. In this case it would be $12.50 per ticket for the upgrade plus the difference in the original ticket price. As far as the buy 4 get 5 promotion I think that's a broker deal and not a Disney deal.