I have a Unity program where all the GameObjects are created programmatically in C#
the camera is the default one that was part of the scene when I created the new project.
...then not "all the GameObjects are created programmatically," if there's at least one (the camera) that's present in the scene before you run. These details matter to the answer, so be sure to always be specific about your situation and what you need.
In this case, once you've modified the camera in the editor's play mode to have the settings you want, you can click on the gear icon at the top-right of the component inspector and choose Copy Component.
After you exit play mode, click on the gear again and select Paste Component Values to overwrite the camera's settings with the ones you copied.
If you need to do this with multiple components, or multiple objects, you can also save the object as a prefab, then apply the changes back to the prefab to save them.