On installation, the configuration files (in /etc, of course; are there
others?) should all be checked into a revision management system, with
a
vendor branch (the upstream versions from devuan) and a local branch
(the versions as adated to local requirrements). Every time an upgrade
makes changes, the appropriate merges should take place. If changes
are too radical, the merge will fail, and manual intervantion should be
mandatory. Deferring the merge resolution whould be possible -- the
revision management system will hold all the details.

Doing this will maximize transparency whe things get complicated, and
leaves the sysadmin the opportunity to back out of configuration changes
manually or make other necessary changes.

-- hendrik