If you're worried about the temper being ruined by a bit of time in a lighter, let alone a much cooler candle, for a vintage nib made of carbon steel, with a common lighter you won't be able to even begin to get it hot enough to take the temper from the metal. Even for a thin strip of metal like a nib, unless you're focusing great heat in a contained environment, you will do nothing but burn off any surface coatings. In the original manufacturing process it took baking the nibs in a very hot oven for hours to soften the nib for stamping and shaping. And then more baking and oil quenching to re-temper them.
While butane theoretically burns at about 1000C, a small lighter will struggle to get to that temperature in all but a very small spot in the flame, and there are far too many opportunities for heat dissipation for the nib to retain enough of it to even get close to the "straw yellow" color that indicates you are beginning to affect the temper.
Now, what they make modern nibs out of, I don't know. But tempered steel, even with all of the "A" and "O" and other varieties, still requires significant and surrounding heat to affect temper or grain alignment. I'm in no fear of my nibs being ruined.
But maybe I'm a bit of an old galoot. My knowledge of steel and tempering comes from hand tool woodworking and we have been known to go so far as to lubricate planes, at times, with tallow, and make our own hide glue from animal bits.
To each their own. Alcohol works well to dissolve shellac, and that was the coating on vintage nibs. It doesn't do quite as well with oils, but along with a wiping will suffice for anything short of high viscosity crude oil.

And if you have any fancy nibs you're ready to throw away because they've been near a flame, feel free to toss my way. I won't say nought, as the old galoots might say.
Actually, I might try an experiment with a couple of cheaper nibs I have to see if I can possibly affect the flexibility of a nib by heating it even for a long time in a lighter flame. I'll report back when I get a chance.