I don't think it's complicated (in my opinion freebsd-update is way more complicated, it just hides lots of stuff, people are just used to it), you just need to adjust the pkg configuration file to point to the release you want, update (i.e. pkg update -f, saying yes to the prompt about versions) and then re-install all packages from at least base and kmods (i.e. pkg upgrade -f -r FreeBSD-base && pkg upgrade -f -r FreeBSD-ports-kmods), ports should work unless you are upgrading between majors (so a simple pkg upgrade -r FreeBSD-ports should be enough).
Out of caution disable loading any kmods in /etc/rc.conf (i.e. amdgpu, i915kms, nvidia etc) then reboot.
If anything goes south, either downgrade (should work locally with what the packages you have in /var/cache/pkg) or if rollback to a previous BE/snapshot and ask for help.
Comparing this with non-rolling Linux distros like debian, rhel clones, etc, the system is very similar with the same caveats.