The "added" officers were junior in authority, and held little or no responsibility. I believe they were supposed to be the officers who would rapidly expand the army in wartime but in peacetime had no troops to command.
In practice after a few years of peace they were more likely officers of no use at all.
There was no direct equivalent in the British army, their unpositioned officers went half-pay and were not kept on a regiments rank list.
With no simple equivalent word available I think its probably best left in Portuguese untranslated, but explained in a footnote.