How can I not snap people's necks (or only snap it a little bit)?

So the wall-punching augmentation (in the Cybernetic Arm Prosthesis augmentation tree) allows you to punch through weak walls, but will automatically have you snap the neck of anyone standing on the other side of them.

Am I correct in assuming this will ruin a pacifist playthrough? Is there any way to do a non-lethal wall-punch and only snap his neck a little bit?

Solution 1:

I've done this trick on my last playthrough, smashing the wall and knocking out the person on the other side. As I expected, I got Pacifist at the end.

So, in short, no, this technique does not disqualify you for Pacifist. That said, the criteria for Pacifist are quite weird, I think the game is designed to be lenient.

Solution 2:

What you can do (instead of wall punching) is to use a revolver with explosive bullets on the wall. It will render the person on the other side unconscious when the wall breaks, instead of killing him (2 rounds AFAIK). It made the Tracer Tong mission extremely easy (playing non-lethal).