Hello Kelley!
Thanks for visiting planDisney with your question!
The Park Hopper option on a multi-day
Disneyland Resort theme park ticket applies to all days on the
ticket. There is no option to add the Park Hopper option on only a single day. But, you may purchase two days as single-day tickets rather than a 2-day ticket. To do this please purchase an individual 1 park per-day ticket and another individual Park Hopper ticket. During the reservation process, you will be asked to select your desired theme park for each day.
Please note, on the day that you use the Park Hopper ticket, you will have the option to hop to the other theme park starting at 11:00 a.m. You will not be required to make another reservation to visit the other park and you may hop back and forth as often as you like. But, as always, theme park admission is subject to attendance availability.
If you think of any more questions, do not hesitate to bring them to us!
Tiffanie