Can a junior enlisted soldier deny corrective action if it is going to be wrongfully used?

If the SFC is in your chain of command, what he says takes precedent, and you should refer the NCO to the SFC. If the SFC isn't in your chain of command and the lower ranking NCO is, do what the NCO in your chain of command told you to do, then explain.

Carry out your last order first, unless it is an unlawful one or someone senior has countermanded it.

Edit: Learn from mistakes, both yours and those of others. If you are an NCO you will remember this and know what to/not to do. The NCO undercut the authority of a SFC and that was wrong unless lives were at stake. He should be getting a one way conversation from the SFC so he learns too. That's assuming the SFC was in your Chain of Command or was filling a billet that gave him the authority to excuse you.

It gets trickier when seniors from other units order folks not in their unit. Technically they have the authority due to seniority, but unless he has spoken with your counterpart leader - one SFC to another, he has a lot of explaining to do to your SFC. Unless you have been appointed over another unit, you don't interfere except in extreme situations. That's how folks get black eyes, if you have strong leadership. You don't feed another man's dogs or discipline his kids unless the situation warrants or he asks you to. At your level you carry out your last order and notify your CofC later.

As a senior NCO if I told you to do something and one of my team leaders told you to do something different than what I had just told you, I would support the decision of what the team leader told you to do. If I heard you questioned him, or used me as an excuse, I would smoke you too. Being a private is the easiest job in the Army. Do what your told. I don't care if you think you've done your part. Keep doing it until someone with some strips whether it be two or six tells you other wise.