replacing with A-19 Halogen bulbs
A 42W bulb is only going to produce 42 Watts of heat (well, a little less since some of the energy escapes as light (roughly 3 - 5% for a halogen)).

So as long as the fixture is rated for at least 42 watts, that bulb will be fine. The max wattage limit should be noted on the fixture somewhere, either on a sticker, or embossed in the metal.

I think your fear of the word "halogen" comes from the number of accidents attributable to 300W and 500W halogen floor lamps with exposed bulbs, these concerns have been mostly addressed with new safety features (primary guards over the bulbs). But a 42W replacement bulb doesn't pose the same hazard.