We have done this in the past, directly e-mailing FIRST and explaining our situation. It was a special occasion and we were allowed to change.
Not sure if they’d repeat that, but, as for the deadline, I don’t believe you could change regionals after you paid for them.
Anyway, not much info, you’re probably better off contacting FIRST HQ.
Your team can sign up for 1 regional (and the CHP if you meet criteria posted) on Oct. 2
Your team can sign up for second regional on Oct. 26 (and CHP)
Your team can sign up for any other regionals, space available on Nov. 9.
You must pay for your 1 regional by Dec. 8. This is non-refundable.
Changes made outside of this system are based on lots of factors, including spaces available. Your team could be put on the wait list. The wait list is NOT published so it may be hard to plan if you want to switch. There were many teams on waitlists last year that never made it off the waitlist.
There was a book I read as a kid called “What if everybody did.” The rules are structured to help prevent this.
Hope this helps and make sure you have all the deadlines posted on the website.
Feel free to contact: firstname.lastname@example.org with your question to get an official reply.