No, you are personally responsible for your actions even when they aren't "the most heinous of acts". Being sworn to uphold an unjust law means that you have no good alternatives available to you: you can break your word (and perhaps lose your income) or you can perpetrate injustice. In that situation you must choose which is the greater wrong.

But the unjust law doesn't need to rise to the level of genocide or war crime before it becomes a greater wrong than breaking your word. I think murdering a single innocent person is worse than breaking your word, for example. How many unjustified deportations does it take? I don't know.