You can change the LUKS passphrase without dataloss, but can you also change the actual key?
I reckon you would have to re-encrypt the whole disk, but that would be acceptable to me.
We are considering distributing a live USB with full disk encryption. But that means that even if you change the passphrase, I will still be able to get the secret key if I got a copy of the original live USB.
So the first time you use it, it should re-encrypt the whole disk with a new key (and not just a new passphrase to unlock the key).