Thanks for your comments.
Here is my reasoning.....
I currently use a Galaxy S3, pending getting the S5 very soon.
When I first got my S3 it seemed perfect. Everything
I have since done a number of Kies updates and also a couple of Sammobile updates via Odin.
Every time I updated, there seemed to be some things that didn't work as well.
So I decided to try and revert to the original
firmware that came with my mobile, via Sammobile and Odin.
I have done this, but now, whenever I leave a wifi zone, my mobile internet seems to connect when it feels like it. Sometimes not at all.
I have to switch mobile internet off, restart the phone and then switch mobile internet back on, to get it to start up.
When I get my new S5, I would like to have an exact copy of the phone, so that I can always revert to my very own original setup if I choose to.
Apparently after updating beyond Android 4.3, there came a change in the format of the EFS folder, which prevented stepping back.
I don't want to be forced into that position again, so want a perfect copy!
From my reading, it appears I would have to root the phone, install Titanium backup, do a full nandroid backup, then unroot the phone and reset the counters to be back in warranty.
Am I right or would that not work?
edit: After updating firmware on a phone, does a factory reset change back to a previous firmware? I would think not. I think it would just reset all the added consumer stuff. (contacts, apps, emails and sms etc)