If I decide I want to install Kitkat is it possible and easy to go back to Jelly Bean 4.3 - as I have only just started getting used to it having been on Android 4.0 last eighteen months so want few days to get used to 4.3 but can I go back to 4.3 easily if I decide to
Thanks
If you are rooted, yes. All you need to do is flash a 4.3 ROM to return back to Jellybean.
If you are not rooted, then you will need to restore the factory image. It's not difficult, though, does require a few downloads and make sure the appropriate drivers are installed on the computer. Here is a general how-to install the stock images for the Nexus 7 (2012). It would be the same for the Nexus 7 (2013), except image files will need to be specific to your device.