If I book a package ...

[Queen of the WDW Scene]

And get 3 day park hoppers can I modify to make it 2 day park hoppers prior to final payment?

 

[Master Yoda]

And get 3 day park hoppers can I modify to make it 2 day park hoppers prior to final payment?

Yes.

The question would be why not just start with a 2-day pass? If a 3-day ticket purchase is required for a promotion then it is quite likely that the promotion would not remain after the change.

 

[Queen of the WDW Scene]

Yes.

The question would be why not just start with a 2-day pass? If a 3-day ticket purchase is required for a promotion then it is quite likely that the promotion would not remain after the change.

Because I'd like to make park reservations for all 3 days from the get go.
Its not a promo.
I usually book a 2 day PH and do the Christmas party but with that up the air I wanted to book a 3 day and then drop it down to my usual 2 day if the dates align and the event seems worth it.