This weekend I did several series - some with JPG's and some with Nikon raw's. Now in LR, the metadata is written to the folders containing the raws as separate XMP files; but for the jpg's it is written into the original files-changing them.

In LR I don't have this option negated, so the metadata updates were written into the JPG's. And I guess LRT writes directly into them as well.

Not sure I like that ... here's the question. I did some experimental work on these sequences and I'd like to reset everything back to the beginning and do it again ... but I don't know what residual metadata changes are lying around in the jpg's that could mess up the sequences going forward. I did try loading them all into LR, and doing a DEVELOP reset and ctrl-S again ... but not sure I have fully reverted them back to out-of-camera.

Now, as it turns out, I do have an original, un-modified backup of the sequence and I will more than likely just swap that back in.

But, what would be the preferred workflow for JPG's so that you could revert ?

thanks, jc

You can always revert by initializing in LRTimelapse and saving. You can as well just clear the meatdata (Ctrl-O) to completely get rid of the XMP data in LRT.
It's Adobes standard to write XMP into the JPGs and not as sidecar files, I'd rather prefer to have sidecar files for jpgs as well - but on the other hand I normally never use JPG for time lapse.

Not sure if this will help, but...

Are you familiar with ExifToolGUI (or even the underlying command line tool, ExifTool)? This should allow you to batch process any metadata changes that are necessary.

Normally all necessary metadata changes can be done in LRTimelapse. With 3.3 you can even shift wrong camera dates.