Hiya, Jamey! Thanks for stopping by planDisney. What a great question you've brought us!
To answer your question, I walked through attempting to switch both a
Magic Key reservation and a
single-day ticket theme park reservation in my upcoming plans to a reservation for today. It appears that it is possible, as long as there are reservations available for that day. You may find that one or both parks may be unavailable when you go to switch. If reservations are fully booked, it won't be possible to switch to a same-day reservation. Though in my experience, I have occasionally seen park reservations become available midday, so it is definitely worth a shot if your flight arrives early enough. I hope this helps!
Jamey, you will be visiting at the start of the
Holidays at the Disneyland Resort. It's the merriest time of year, and I'm so excited for you to experience it! There was even snow on Sleeping Beauty Castle today, so I can't wait to see the resort fully transform. Be sure to catch some of the seasonal entertainment offerings.
A Christmas Fantasy Parade is one of my personal favorites, and the ride overlays at
Haunted Mansion Holiday and
"it's a small world" Holiday are must-sees. Check ride wait times and performance times in the
Disneyland Mobile App.
One last tip for your trip: Keep an eye on the
Disney Parks Blog for the Holiday Foodie Guide - it's the best way to plan which seasonal snacks you want to try during your visit, and I expect to see it released any day now!
I hope this information helps you plan a most magical visit, Jamey.
Please let me know if you have any other questions, and we will see you real soon!
Wishing you magical merry-making,
Melissa