Preview environment questions

I’m looking at preview environments but I’m not sure if/how to do a couple of things:

  1. I have a 3rd party managed OpenSearch provider in use on production, for previews I would be fine to have OpenSearch spun up from a docker image. Is it possible to have preview only specific services.
  2. The env variables are coming from an environment group, I’ll need some to be overridden/different for preview env, how can I do that? Ideally having a preview environment group would be best.