Hi Jimmy, welcome to planDisney!
You picked the perfect day to kick off your magical vacation, as the
Lunar New Year Special Event at
Disney California Adventure Park begins on January 21, 2022! If this is anything like the Lunar New Year events in the past, you're going to have blast!
But to focus on your question, it is possible to change your starting theme park even after tickets have been purchased. However, to do this, you will need to cancel your current theme park reservation and book a new reservation with the starting theme park of your choice. There is always the risk that reservations become completely booked, so I highly recommend viewing the
Theme Park Reservation Availability Calendar before canceling your current reservations! The GOOD NEWS is that I just checked the reservation availability calendar, and both
Disneyland Park and Disney California Adventure Park have availabilities on January 21, 2022, for both One Park Per Day Ticket Guests and Park Hopper Ticket Guests!
To cancel your current theme park reservation, you'll need to log in to your Disneyland Resort account and select the "My Disneyland" link. Then go ahead and click the "Ticket and Reservation Details" link and select the "Cancel Reservation" option. Once canceled, you're free to go ahead and book your new reservation!
Super excited for you, please come back if you have any more questions!
See ya real soon!
Jin