Result is this mod, it can override the screen area used by the eye accomodation, the eye accomodation parameters like speed & range and also color toning parameters from the game. The new default parameters in the mod config make the eye accomodation changes almost invisible and also reduce the color toning and contrast for more realistic looking colors. They look good at least with the Vive Pro.
Download from here.
Read the readme for instructions how to install and configure it.
Video showing it in action, note the lack of visible brightness changes: https://youtu.be/c3ew2zCGULE