Ratel
As there are always changes to the OOBs in these patches it is never a good idea to patch-up with on going games.
I create a new installation of the game and patch that up so you can at least get new games going in 4.0 while you run out the older games on 3.5
Having two instals is no problem, you just need to give the game a new folder inside the Camo Workshop folder in your C drive.
C:\Program Files\Shrapnel Games\The Camo Workshop\ as many versions of the games as you want
You can just copy the entire ww2 v3.5 folder to a new folder, call it 4.0 and then apply the patch to that folder during when it prompts you during the instal of the patch.
easy
I have MBT 4.5, and two versions of ww2 v3.5 going at the moment... and will be making a new one for 4.0 in a few moments.
Have fun