You could probably alter small things, but there is probably a hard limit of what can and can't be done. A better use of the energy would be to save the people who got murdered at the death camps. There's a really cool episode from the 90s outer limits where a time traveler helps a lawyer try and prosecute a former German death camp guard.

What's bad about pouring in boiling water?

I've seen this before, and the set up is pretty similar.