Originally Posted by Marc Sabatella 
It would have to be an exceedingly poorly written program to decode and then recompress an image just to write some tags. If the program is anything that ever gets mentioned here, I'm sure it's fine.
Well, my experience with the code written I've seen over the last few decades, you can not be sure. It is not all quality that's out there
I'd say: it depends on the program you are using. Try: "Save as...", close and open the saved file, then save it again, 20 times.
Then pixel peep the first input file versus the last output file. Examen the result.
- Bert