oooh that's very interesting, for backup reasons but also I am working on a combined template for all our sites and I REALLY would like to test it first, so could I clone a existing network and use it as a test platform? - I want to see exactly what settings will get changed when the template is applied.
@Adrian4 as @alemabrahao said, you can just combine the wireless network into the existing combined network. I've split and combined networks probably about a hundred times and the only thing you lose are client statistics and possibly custom client labels. No configuration is lost and network traffic is not interrupted.
I am unable to combine the wireless network with the combined network (the combined network does not appear as an option).
I think this is because the combined network doesn't have the wireless part - This was the reasoning behind splitting the combined network first.
However I got around this by adding a new AP to the combined network from inventory which created the wireless bit and after that combining networks was an option - but to be honest I think I will just move the access points to the combined network and then bin the old wireless network.
@Adrian4 it is actually the other way round. If you were able to add an AP to the combined network, then it already included a wireless network. It isn't always obvious that this is the case, but if you look at the firmware upgrades page, you should see what element make up the combined network there as they are split out on that screen.