I was deploying some dotnet app and it broke because the devs baked a config key into the image that was otherwise unset, which enabled it trying to start a SSL endpoint without a cert, thus breaking the app.

Are you talking about altering environment variables in a system, or altering software to read different environment variables? I read jt2190 as talking about the former.

I don’t use env variables for this and many other reasons. They seem like a spectacularly bad idea for config, as the op noted.

I’m talking about altering a config which you control - adding to a config is pretty risk free if it is your program, altering a config of course is not.