Is there a way to change the difficulty in the middle of a campaign?

[Tomislav Uzelac]

There is no ready-made way to change the difficulty within the game.

You can edit the savegame if you want to: go to the saved games folder, and open the savegame with 7-Zip or a similar program (the savegame is a zip file, essentially).

Within the savegame, there will be a file named "main.yml": open it (with notepad) and change the line that says "level: classic" to "level: easy" or "level: normal" - however you like it.

Cheers!