Have Mp3tag set file to read-only after saving changes?

A lot of my mp3 tags keep getting modified (erased TitleSort and ArtistSort tags). I have narrowed down the suspects entirely to Windows 7 / Windows Media Player 12. I tried uninstalling WMP, but found I needed it for media center / TV tuner capabilities. I tried removing My Music folder from the Music library as well, but one wrong click and tags go boom again.

Is it possible to have Mp3tag set files to read-only after saving tags?

No, but what you can do is to set the files to read-only in Windows Explorer.

Check the settings of 1) WMP so that it does not look for track information automatically in the Internet.
2) if you can, set your firewall so that wmp is not allowed to access the internet.
This should leave your tags alone.
BTW: I have not heard that WMP really deletes tags... Ususally all the libraries are so badly filled that you can be glad if it finds a track and artist....

That's what I've been doing.. but is it possible to code such a feature into Mp3tag?

Trust me: everything is off. Do a google on WMP12/Windows 7 and redoing tags - you'll find tons of complaints, even on Microsoft's forums, and their engineers don't know jack shit about how to fix it.

And yes, WMP12 is erasing TitleSortOrder, ArtistSortOrder, AlbumSortOrder, etc. Microsoft has never supported these tags and apparently thinks it's nice to scrub your files of them in certain situations.