Say you install FreeBSD 12.1, you can keep your package system using the 12.1 package set forever. No updates will be available. But they'll always work.

In /etc/pkg/FreeBSD.conf you will find something like this: > url: "pkg+http://pkg.FreeBSD.org/${ABI}/quarterly", Assuming using amd64 that maps to: https://pkg.freebsd.org/FreeBSD:12:amd64/ There you can see there are "release_X" sets that map to 12.0 12.1 12.2 12.3. Again, no updates will ever be published on those but they will be guaranteed to continue working so long as they don't get deleted.

The FreeBSD community just doesn't have the manpower (of volunteers) or willpower to maintain what you're asking for.