Similar question here: https://www.disboards.com/threads/magical-express-question.3627934/
Answer: You may do that 100%
Tried to call MS yesterday to book Magic Express as the online order form requires flight information. Message said that they are assisting guests displaced by hurricane Irma and if I don't have a reservation in the next 7 days please call back at another time.
Can I just go to the magic express desk at the airport without a reservation?