Change encrypted partition UUID

For changing the file system UUID you have to decrypt /dev/sda1 and then run tune2fs on the decrypted device mapper device.

sda1 itself does not have a UUID thus it cannot be changed.

The LUKS volume within sda1 does have a UUID (which is of limited use because you probably cannot use it for mounting), though. It can be changed with

cryptsetup luksUUID /dev/sda1 --uuid "$newuuid"

To change the UUID of the LUKS volume, use cryptsetup luksUUID --uuid=<the new UUID> /dev/sda1.