Yes, I had to call them to get it done and my only complaint would be the 35+ minute wait before the call was answered, but I understand how busy things are currently.
You can it's fairly easy
That shouldn't be a problem. They have been very understanding of issues like that.
Like Renee said, when I was at the park Monday they told me a daily ticket I had was good for any day, I didn't have to use it that specific day. I think they just encourage you to so they can keep tabs on guest flow.
I was told that the tickets were good for the entire season if you choose to go on a different date.
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