to get all the difficulty achievements
start a new game and open the cheats window
with press enter
the cheats are
/achievements set DIFFICULTY0_VICTORY
/achievements set DIFFICULTY1_VICTORY
/achievements set DIFFICULTY2_VICTORY
/achievements set DIFFICULTY3_VICTORY
/achievements set DIFFICULTY4_VICTORY
/achievements set DIFFICULTY5_VICTORY
/achievements set DIFFICULTY6_VICTORY
Here are all other cheats credits goes to the ta Community
Achievement guide (console commands)