I use the Nebula skin and after doing the upgrade - much (but not all) of the customisations I made appear to have been reset back to the default - is this going to be a feature of upgrading?
The upgrade from RC1 to RC2 will not have any effect on Skins other than the OSMC skin. I use Black Glass Nova myself and have not seen any changes when upgrading OSMC.
However, I did notice that an update to Nebula was released yesterday as I have it installed but not active on one of my boxes and saw the update occur.
If you had directly edited the source files for Nebula you would lose your changes when the skin auto updated.
The only way to avoid this happening is to turn off automatic add on updates in Kodi - set it to notify instead, then you can pick and choose what addons to upgrade.
Thanks for that - I didnt realise that addon updates were set seperately - I have auto update for Kodi set to off but obviously it updated the skin, would have thought that it would have honoured customisations (no changes to source) backgrounds home menu etc
So you didn’t customise the actual source code of the skin then ?
Whether a skin upgrade affects your normal skin settings (not source code customisations) is entirely up to the skin author - if it’s only a minor update then it usually wouldn’t, but if the skin had a major redesign with different layouts, changes in functionality or adding/removing preference settings then it could well lose some of your custom settings.
It might be worth checking in the support forum for Nebula:
http://forum.kodi.tv/forumdisplay.php?fid=211
If Auto Updates is Off in Kodi itself (unrelated to the update settings in OSMC settings) in theory it shouldn’t update an addon without your permission but I think there are some bugs around this as I have heard of updates to addons happening anyway.
So you didn’t customise the actual source code of the skin then ?
No, no changes to source
I had Kodi auto updates off and just checked the addons and sure enough it automatically updated the nebula skin 23/4 at 10 so kodi is still allowing updates to addon (if not itself) 
set to notify now
Thought so.
Just to be clear - Kodi never updates itself - there is a version check addon installed by default in Kodi (although I think we may disable that in the OSMC build of Kodi) which checks for new versions of Kodi but it is unable to update itself - it simply displays an alert that a new version of Kodi is available to download.
On OSMC Kodi updates are handled by our APT based update system, which runs outside of Kodi. The OSMC settings addon checks for new APT updates and downloads them to give a nice user interface, but the actual upgrade of Kodi happens after it has exited. (The blue update screen)
Kodi addons on the other hand have their own built in upgrade mechanism in Kodi based around Kodi repositories. When you install an addon via a repository Kodi will periodically (every day ?) check the repositories for new versions of the installed addons, when it finds them it will by default just go ahead and upgrade them on the fly, pretty much any time that you are not actively playing video. This addon upgrade system is on all Kodi platforms not just OSMC.
We do, because it checks ‘xbmc’ package (designed for Ubuntu I assume) rather naively. It actually invokes apt now and installs a new build, so it is good we disabled that
S