Thanks for your answer... I was just thinking about the worst case scenario since nandroid is the fastest way to get it back to how it was before but there is always the manual backup using Titanium Backup of each app manually.The partition table was changed between JB and KK, along with the bootloader. That being said, what you want is this:
*READ FULLY before touching anything*. It is not my utility and it's not something I've used but appears to do what you want.
Be aware that your nandroid isn't going to help you in this situation.
I thought one can do it in this way using the utility you mentioned and it will still work..
Use the utility and then go back to a stock rooted 4.1.2 along with replacing the recovery with something that can handle nandroid. then restore the nandroid. That would seem to work since wouldn't getting back to a working stock rooted 4.1.2 already have basically brought the partition and the bootloader back to JB?
---------- Post added at 10:26 AM ---------- Previous post was at 10:23 AM ----------
Just curious but what kind of kk update problems were you having? Verizon sent me a Certified Like New Replacement a few weeks ago and it came with JB and I did the OTA to KK without problems but that phone has been sent back as I only needed to swap the battery and the lower half out since it seems every 7-10 months since I got the original phone, my battery has always gotten swollen and knocked out the back cover.First time using XDA. I've had the same kk update problem as a lot of ppl it seems. This tool worked like a charm. Many thanks Bwen and keep up the great work !