I beg you, if you are a developer of an open source app or program - add screenshots of your app to the README file. When looking for the perfect app, I had to install dozens of them just to see what the user interface looked like and whether it suits me. This will allow users to decide if the app they choose will suit them… Please, don’t think about it, just do it…
Ding ding ding!
That said, the solution is to set new defaults for new installations only and not change existing configs. Users lose their minds (rightfully so) if you modify their existing configs.