I would like to ensure (or be assured) that roon will not update any of my music files. No tag updates, no embedding of images, no use counts, no audio normalization, nothing. Is this possible other than by making my files and/or server mounts read-only?
Roon does not update your files with any information, it stores everything in its own database. So I am not sure what feature you are requesting.
The only change Roon can make to your files is delete them, if and only if you explicitly request it to.
If roon can/does update any files, I would like a feature/option that would disable this behavior by marking a folder read-only (to roon) in the Storage settings.
See the Knowledge Base page on Watched Folders:
…Your files are left in the folder and won’t be copied or modified in any way, unless you explicitly choose to add or delete them from your library…
…Roon will scan the folder and add any music it finds to your library without moving or changing the files at all.