Peace to you,
in a war, sure. There is an Adversary going around seeking to devour us, hoping batter us (the sifting process of wheat) enough that we are damaged, even destroyed, his accusation against man is that a man will give all he has to save his own skin, including to 'curse God and die'. He is also the father of lies and there are a lot of lies in this world, and in religions.
Paul describes the armor that we need and should put on (and why we need it). The sword is truth (and yes it is interesting that the word 'word' is in sword, considering verse 17 in the green text... though that could just be a coincidence that applies only in English, like devil has the word evil in it).
The phrase you use 'engaging in warfare' doesn't sit quite right to me. Something just seems off to me about that. Perhaps because it implies going out and looking for a fight, and not something that comes from love. Perhaps because you seem to have placed a negative connotation to it, as if a Christian is doing wrong (or going against Christ) by bearing witness to Him, and to His words, even knowing that may bring opposition? Or perhaps I simply misunderstand what you mean when you say 'engaging in warfare'. This is why I asked.
Some battles are friendly, but they are still battles.
Then there should not be an issue with wishing someone peace, even if on opposite sides of a debate, even in disagreement, right?