Good day, Wade!
Welcome to planDisney! Thank you for bringing your question to us!
It may be possible to upgrade your One Park Per Day
Theme Park Ticket to include the Park Hopper Option. But, you must request this change at the
Disneyland Resort Main Entrance Ticket Booth. This upgrade is subject to availability. So, you may want to check first to see if the Park Hopper Ticket
Availability Calendar has available
Theme Park Reservations on the day of your visit.
If you are able to upgrade to a 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 Theme Park Reservation in order to visit the other park. And, you may hop back and forth as often as you like (subject to attendance availability.)
If you have more questions, please head back to planDisney!
Tiffanie