A K.u.k. Feldpost Question

The Austro-Hungarian Military Mail system (K.u.K. Feldpost) was, we are told, "a 'common army facility', the task of which was to convey all official and private consignments ('letters, correspondence cards, newspapers, merchandise, parcels') between the army in the field and the home."

But, did it also serve as an "occupation postal service," available also to civilian populations in the occupied regions?

I ask this particularly in regard to the overprinted issues from Romania and Italy, which are re-denominated in the local currency. For strictly army use, that wound seem unnecessary. And what about in Austrian occupied Russian Poland (the Militargeneralgouvernement), where there were no specifically overprinted issues?