How about dual FS installations?
You could use Golden Wings to fly in the pre-war years, and a "stock" FS9 set up for the post war years, using the Cal Classics AI package and some of their airports (like Lisbon.)
For my post-war sim I took the Cal Classics AI package, which is meant to depict the world around 1959, and backdated it by replacing all the turboprops (eg., Viscounts) with DC-3 and DC-4 variants. Then you could add your own military AI, with appropriate planes for each sim.
There are lots of pre-WW2 European planes out there, and a lot of post-war planes too. For both pre- and post-war types you might start by checking Classic British Files.