On PC: You can get this legit or you can use console commands.
Press the tilde (~) to open the console.
"rewardKarma -500" (without quotes), will take you from neutral karma to bad karma (minus 1000 if your on good karma).
Then enter "player.setlevel 20" (again without quotes). Leave the console and wait for a bit and the achievements will unlock.
On Xbox: Get to good Karma, then just before you finish a quest to get to level 20, either go on a small killing spree to get ot neutral or a big killing spree to get to bad. Keep reloading the save until you have all three achievements for that level. This way you don't have to play thourgh it more than once.