The only way a ai-unit will walk around with a lowered weapon at the moment is when he is set to careless or relax mode.
But this will also effect the units abillity to walk in formation and its spotting Beahviour.
In aware mode their are only walk around with raised weapons (besides running/jogging) wich looks realy unrealistic and could be changed with that new command. (try to walk or run a few kilometers with your rife raised all the time, its impossible)