If i purchase 6 park hopper tickets through a 3rd party seller such as Boardwalk Ticketing or Undercover Tourist (via the ticket calculator link Touring Plans provides) and then while I am at the parks, decide to add on an additional park hopper day ticket, will I have to pay full price through disney or will I get the prorated rate I received for buying six tickets at once?
I don’t know exactly.
But you would be paying to upgrade all days to park hoppers. Or you buy a single park hopper day ticket. You can’t just upgrade one day.
Edit: my bad. Didn’t read the OP post properly!
It will take me a minute to parse this, bear with me.
If I read you correctly, you purchased park hopper tickets (6 of them) of multiple days, from a reputable offsite broker, and you may wish to add-a-day.
If you’ve used part but not all of your benefit, you should be able to add days in-park to whichever tickets you like, for the same charge as upgrading a standard Disney ticket for one additional day. Because your tickets are already for park hopping, there would be no more charge to add park hopping, just the park-hopping day charge (rather than if you were upgrading one-park-per-day tickets with a park hopper day, it would be the day fee plus the park hopper fee for the length of ticket).
You’re not (necessarily) getting a discount for buying 6 tickets at once, you’re getting it because you’re buying from a broker.
I hope that makes sense, and I answered your question.
Thank you for your help! I actually was able to find 6 day park hopper with a 7th day free through Undercover Tourist! So now I don’t have to worry about working out the logistics if we want to add on another day! yay!