The game is a sandbox. You can customize as you like. I add 3 Officers (and dogs) from the Résistance set to the initial enemy pool. (Instead of the normal three special units.)
The 7 special units on the table (at start of game) are replaced by SS-ers from KickStarter. Same rules but correcter storywise for me...
This is what to follow. This game is a WW2 close quarters combat cooperative sandbox puzzle in a box.
I highly recommend to play with just base game content at first. Otherwise you run a high risk of combining something without understanding the consequences of it.