Your original raw files and the DNG files both contain precisely the same raw image data. So what do you expect to gain by trying to go back to the original files? My suggestion would be to just leave the DNG files as they are, and then start working with the CR2 files after you upgrade. You aren't going to see any difference at all in quality. But if you want to take the time to match the DNGs to the CR2 files and then copy the metadata and adjustments, go ahead. In my opinion, however, it's just an exercise in futility.
I agree with the above post.
All DNG files store the edits you have already done on those older images inside the actual DNG file. So if you delete them all edits will be gone. They will not be transferred over to the originals. LR sees the DNGs and the originals as 2 completely different images even though they may be of the same subject and have like file names except for the extension.
That comment is just slightly misleading. Lightroom does not automatically save edits inside of DNG files any more than it automatically saves changes to proprietary raw files in XMP files. The default method for saving changes to proprietary raw files, DNG files, JPEG files, TIF files, etc., is to save them in the catalog. And it's necessary to specifically make a change in preferences in order to have those changes saved to the file. But even then, not everything gets saved, and it can become confusing. I still feel that the best way to handle things is to let the catalog be the crucial file in Lightroom that stores all the adjustments. It's just a vital that the catalog is protected and backed up on a routine basis.
Doesn't really matter where the edits are saved. They won't be carried over to the originals as LR see those as separate files as stated in my first post.
I disagree in letting the catalog be the only place to store edits. To each their own.
I've been using Lightroom since early in version 2, and the catalog has never failed me. But like you say, to each his own.
If you really wish to proceed with using the CR2 files instead of the DNG files you could use John Beardsworth's Syncomatic plugin to sync edits from the DNG files to the Raw files.
Import CR2 files to same folder
Run Syncomatic and select the metadata you want to sync.
Use Lightroom to sync cropping (the plugin cannot perform this step)
Remove your DNG files from Lightroom after confirming everything is sync'd
Note: Besides not being able to sync the crop settings for the files this process also removes all of your history steps (you just get the final state of the file)
History just shows as "import date/time" and a new history step "temp".
That's fine if you don't use ACR also. I do so I want the edits store from both LR and ACR to be read by the other.
Uhm, I know that there is a controversial discussion about whether original RAW files or converted DNG files are better. I chose to stay with originals. Only they're not supported in the older Lr version.
It seems like there's no easy solution to this. I've found file names in the catalogue database. I think I'll just try my luck with that. (I work with SQL databases almost every day.)
Well, for what it's worth, I don't convert to DNG on a regular basis. The only time I do convert is usually when I don't have support for a camera. And that really isn't very often. I'm not arguing which is better, DNG or native raw files. I'm just saying that it's going to be an exercise in futility (in my opinion) to worry about switching the DNG files that you have already done. But that is your choice. If you want to take time to try to match up the adjustments, go for it.
As stated, earlier, John Beardsworth's Syncomatic plugin will do what you want, I believe, although use the 10-image-limited trial to make sure: Syncomatic - Sync files with same name or time
As far as changing names of file extensions in the database, I wouldn't necessarily assume that DNGs are handled identically, so changing the names is not a guarantee that things will work entirely the same--things like crop origin or number of pixels might be different, so it seems like a plug-in that actually uses LR's API to do things would work more reliably.