Isn't the answer to 2 to have a pre-production environment to calculate the diffs/changesets/etc against, or even to deploy the change to to test it? I know wit

Isn't the answer to 2 to have a pre-production environment to calculate the diffs/changesets/etc against, or even to deploy the change to to test it? I know with CloudFormation, for all its faults, is pretty good at making a hypothetical changeset before it runs, and if that's not safe enough, you can just deploy it to your dev environment and use the changes succeeding and your service being up as a integration test.