Linode OS Upgrade via /var partition reuse

I have a separate /var partition for my data, and all of my user-generated stuff (Sandstorm, email, databases for things) lives there.

• Make a new OS image. I was going from 16.04 to 18.04.
• Make a new boot profile for the image. Include the new OS image and /var.
• Boot into single user mode.
• Mount the old /var on /mnt
• Move /mnt/var/lib/dpkg somewhere else
• cp /var/lib/dpkg /mnt/var/lib/dpkg
• Edit /etc/fstab to mount /var on boot.
• Reboot
• Docker container should theoretically come right back up once Docker is reinstalled.
• I have Sandstorm installed on /var/sandstorm
  • Move /var/standstorm to /var/sandstorm-old
  • Reinstall Sandstorm, then stop it
  • Move /var/sandstorm/var away
  • cp -av /var/sandstorm-old/var /var/sandstorm
  • Restart Sandstorm