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.
Background
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).
luksFormat
on first boot of the media, ideally as late as possible (to allow for early boot entropy collection), which files can be stored on.