it takes me a day with hacks.. but.
if your doing it legit you can do it in 1 playthrough, make sure when you do the first mission it selects your reccomended difficulty to hard.
after each mission you do for good/ bad karma load the autosave immediately after you do the mission

therefore you get the opposite trophy.
theres a mission where your on a train now for that do the same thing, but to get good/ bad you have to be one.. beat that on one... load the autosave... kill a few people... or save a few.. then do the mission, do the same thing for the trish mission at the hospital
If his doesn't make sense I'm sorry
basically just after each mission that has a trophy load the autosave

then you can have another attempt at that mission

and because you did it on hard once you beat the game you get that trophy too