The Rule of Thumb I worked by in film days was that you can change the presentation of the image (exposure, dodging, burning, time in bath); you do not alter content (adding, removing, or manipulating elements of the picture).
100% this. The fact that you're photographing it already means the camera (focal length, aperture, format size, composition, exposure, etc.) is impacting the scene. Fill flash is fine.
The Associated Press will fire you for burning and dodging these days
That, IMO, is ridiculous.
Fill Flash

