Best way to amend EnvVars for specific configd service?

[cluck]

I would like to enforce environment variables on specific configd services and all their actions.

I had some success by manually editing /usr/local/opnsense/service/conf/actions.d/actions_<service>.conf files and rc.d files (pre-pending '/usr/bin/env VARIABLE=value ' to commands), but this isn't viable for all action types and gets lost after updates.

Is there a more permanent way to do this?

I first thought that /usr/local/opnsense/service/conf/configd.conf.d/ is what I was searching, but these affect *all* services.

If you wonder, my immediate usecase  is acmeclient: I would like to override DNS resolvers with CURLOPT_DNS_SERVERS, such that it doesn't end up querying the nameservers from /etc/resolv.conf (which leaks the internal DNS view, breaking DNS-01 challenge preparation).