plausible concept. However, since jpeg files deteriorate with each successive write to the disk, it’s impractical. If you are not extremely careful, the final image could look “over-processed” compared to the original.
Attempting to successfully edit a poor jpeg is akin to RECOOKING an overdone turkey dinner with more gravy and spices – you’ll taste the spice and sauces, but in the end, the meat will still be way overdone.
Ask for the RAW image, pull it into LR5 and turn out a masterpiece (assuming you started an image that is halfway decent). 🙂