OK, maybe at cross purposes. Here is what I understand goes on with the config file.
If it is NOT read only:
When you start the sim, the settings are loaded. If you make changes in the sim, those changes take effect for that session (until you close the sim) and are written to the config file so that they persist to the next session.
If the file IS read only:
When you start the sim, the settings are loaded. If you make changes in the sim, those changes take effect for that session (until you close the sim) BUT are NOT written to the config file and they don’t persist to the next session.
I don’t know what happens if you change the file WHILST the sim is running (which is what I think you did here from your post above).
If you have LODs set as 9 with the file read only, they will be 9 in the sim as long as you don’t make any changes to the graphics settings. Note that if you make any graphics settings changes, the graphics settings shown in the UI will be applied for the remainder of that session. So to keep LOD 9, you must not make any changes to the graphics settings at all [note that there may be some settings that don’t do this, e.g. data settings etc - I;ve not tried them all]
By the way, this is how people are saying they are getting 30+ FPS with LOD 9 - becuase they aren’t actually seeing LOD 9 at all - they’ve checked the graphics settings or made some other change that means the sim resets the LODs to whatever is shown in the UI.
If the file is read only when you start the sim after the update, it cannot add the new off screen cache setting to the config file - but I see it has now done that, so that setting will now take effect.
Hope that helps