To rename a cryptsetup luks volume that's used during boot:

dmsetup rename oldname newname
edit your fstab and crypttab to use the new name
dpkg-reconfigure linux-image-(your kernel version)
(or run updateinitramfs directly)

Keywords:

during update-initramfs:
WARNING: cryptsetup: failed to determine cipher modules to load for /dev/mapper/(root device name)