Given that USERID exists for the --userid parameter, which was deprecated, I think this should instead (or additionally) check for the UserID being defined in --extra-config, and if not, appending the corresponding line; similar to --processid.
Same nit-pick as for __opendkim, I'd suggest using alphabetical sorting.
Rather than add more parameters to the type (we don't want to support 100% of the .conf), I'd propose we rely on --custom-config instead.
I'd probably propose we keep only the *) case, or we leave DIRECTORY="/var/db/dkim/" outside of the case block, and only keep the 'debian') case.
Closing this MR as gitea borked it when updating it.
Anyway, adding this comment to the manifest:
# Due to the way rc.conf works on *BSD, we find ourselves in the awkward
# situation, where a…Will you do the rebase/conflict resolution? or should I do that and test changes?