Hello @KevinSull.
“read only” is the issue.
and won’t allow any changes to be saved even via the gui
correct.
If you are not sure what the change suggested by other users do, try to clarify or ask if these changes can have problematic sideeffects and proceed with caution as you do changes at your own risk. If you are unsure and the change is not essential, I strongly recommend to not change any MSFS files.