Definitely impossible to change difficulty of an underway campaign?

[Drozdov]

Glad to hear the team are taking notice. I think you should allow difficulty changes during a campaign without any limitations, though that might not be so easy to allow if the whole game isn't designed to do it. Yes, some people might prefer not to have the temptation of lowering the difficulty, but in general it causes more trouble than it's worth.

I did make back-ups of the campaign before patching (think I have all the right bits). Reinstalling and reverting is obviously an option but I'd like to use some of the new patch features (really like that you can now have the proper mission flight path on your map without also having plane icons, it's much more sensible and realistic).