Hi, Adam

Firstly, I would like to sincerely apologize for the delayed response as we have been experiencing an unusually high number of tickets. I am sorry that it has taken longer than usual to respond to your concern and your patience is highly appreciated.

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Yes, you can add custom fields to the form to do this.

The Custom Fields feature gives you the option to add more fields to your booking form so as to customize it to best match your business needs. The customer’s first and last name, email address, and phone number are there by default, but with the Custom Fields feature you can add extra fields if you want to ask a customer a question, collect additional personal details, or for any other reason.

Please check this page showing how to do that , in details - 

https://wpamelia.com/custom-fields/

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Regarding allowing customers to cancel or reschedule, you have to set a customer Panel for them, and allow them to do this - in Role settings :

Please check more details on how to set Customer Panel on this page;

You could also allow customers access to do this from the WP back-end, if you wish. More on that on this section of the page.

Let me know if anything is not clear, and if you need further help about anything. Thank you.