I am about to make a tag change to a large number of files and would like to retain the option to revert them back later if I don't like the result. Can I do this by exporting a playlist of these files before making any edits?
As I understand, the playlist would contain all the current tags for each file. I'd then have the option to later load the playlist and "Save" the tags back to the files restoring their original values.
Can someone confirm? Thanks.
A playlist is simply a text file containing the names of your tracks.
Playlists do not contain any tag values.
You would need to export your tag values, including embedded cover art.
The simplest solution:
Back up your tracks before making any changes. This is the most secure way to ensure that your current data can be fully restored.
Thanks for your reply. It's 168GB of files, so I was trying to avoid making a copy.
I understand now that playlist alone would not work. Sounds like it would require a combination of playlist (to load the subset of files) and export (to later "import" the tags back to their initial state). Does that sound like a process that would work?
What would be the correct export format to use?
Please take a look at the documentation on Export that has already been linked:
There is no "Export all tag values" option.
You need to define which field names you actually have and which are important enough to keep. Don't forget to export the cover art separately:
Even if it requires 168 GB of space, I would still recommend backing up your files. 
Just imagine: you "destroy" your TITLE content and, unfortunately, you forgot to export it....
You can get a 256GB USB drive for $30-$40 bucks (depending on speed). It's worth it to have a good backup of what I assume is hundreds of hours of work you've done.
You can use it regardless of a big change or not. Backup once a month or so, you'll never lose more than a few weeks of work.
Another option is apply the changes to a smaller amount of your files, say 10GB's worth or 1,000 files at a time then have a thorough inspection. If you're not sure about the changes, you can Undo CTRL+Z and it shouldn't take too long to revert.
Once you get a good flow going and pick up on specific issues to look out for in your files, you can bump up to bigger batches until it's all done.
Thanks for all the suggestions. I probably will make a backup as it is the safest option.
You can copy the current contents to a unique field name. Once you decide you are keeping the new content you can simply select all files and delete the temporary field. Or move the old contents back if you decide you don't want to keep the changes.