I'm pretty sure this wont work on a transactional system (such as Kubic, CaaSP, or the Transactional Server role on SLE 15 SP1, Leap, or Tumbleweed)

Hm, you're removing the %pre scriptlet entirely, but add new Requires(pre)? Somehow I'm missing something.

I agree with Richard: The netconfig post script will not have the intended effect on transactional systems. The reason is that /var is not mounted into the update environment (because that would actually change the state of the currently running system).

The common way to solve this is to write a systemd unit handling the migration.

This was introduced in https://github.com/openSUSE/sysconfig/pull/18/commits/6f3c5aad8122ce83f35255adb499131838161bf3, but with today's transactional systems this will break. A (temporary) rollback can be found in https://build.opensuse.org/package/show/home:fos:branches:openSUSE:Factory/sysconfig.

common agreement is that the move from /var/adm to /var/lib does more harm than good, so I will hotpatch the revert in Factory. In the hope that Marius and Thorsten's team will sort out a solution next week

IMO we don't need another solution -- the /var/adm (and /var/lib) directory are not used any more, except to migrate from from file + md5 to a link.

I'm going to merge the openSUSE:Factory changes reverting the move to git and resubmit it.