@shylarah Lėo Major, the man responsible for the liberation of Zwolle, twice decorated with the DSO, but refused the first, because reasons (read: Bernard Law Montgomery would have handed him the medal, but Major disliked the man).
As for the Karabiners, I'd make them train with both a Springfield and a Karabiner. Also, a scoped Garand is also an option for short-to-medium distances, as it has one clear advantage on the Kar 98k. Of course, I will not force to pick an American weapon, but think about it. And what kind of modifications are we speaking of?
@ONL I had in mind that we started with standard gear, i.e. Garands, Stens and B.A.R.s, but weapons can also be procured on site. If your character, for example, finds himself cold on ammunition, just pick a dead enemy's weapon.