Thanks for all the help - just did 5 albums and it all worked fine.
1. Backup library
2. Insert CD
3. Make sure the file names will be the same as your existing files (don't worry about the tags, it's just the filename that is important)
4. Delete your old files (otherwise MC will not overwrite the files)
5. Rip the CD
6. Restore the library
7. Highlight all the new tracks and "Update tags from library"
8. Highlight all the new tracks and "Update library from tags" (this step is necessary to update the new bitrate)
Also the file format can be changed, if the filename extensions are replaced with the "Find and Replace" tool. When doing the number "7." MC somehow checks the format and writes the tags in the right format even the old "File Type" tags are still visible in the library. E.g. it doesn't write ID3 tags to files, which should have APE or OGG tags.
However, this should be tried with some test files first before doing masses. And it won't hurt to have backups of the music files too.
This is a rather complex yet standardized procedure. It would be nice if J River could automate those steps and offer it as a feature of its own such as "re-rip cd" in Action Window
A good idea. Though the tracks from the CDs are not tied together anyhow after they are ripped and imported. There can be similarity in the file tags, but that is not always so.
Mayby a tool for copying all the library fields from the file A to the file B could be possible (it should save also playcounts and dates and send the file A to the Recycle Bin during the process).