When you say you "renamed an album" do you mean you did it while editing tags, or while using the "rename, move, copy" tool? If you mean the latter, Jim's advice is correct.
If you just mean editing the tags (which it sounds like might be the case), you can probably fix most of it.
You probably have MC set to automatically write info to the tags in the file. So your error wrote the incorrect info to some number of your files (presumably in the time between when you did it and realized your mistake), which is why reimporting is changing the info (because that's what's in the files now).
Try this:
1) Temporarily turn off auto-import
2) Restore your Library backup from before the goof
3) Confirm that all the metadata is correct in JRiver
4) Select a few files and run Library Tool--> "Update Tags (from Library)"
5) Confirm that the correct metadata is still displayed for those files.
6) Repeat step 4) for all files (you can do them all at once after you're sure it will work correctly)
7) Now try running an import.
If it was just a tags issue the import shouldn't disturb any of the files already in the library, and all the files (except for files you imported after the library backup) should now have correct metadata. You'll need to manually fix the newer files.
To be clear, if you did this with the "rename, move, copy" tool the above method won't work, you'll need to fix that will other library tools.
