I have run the gas lines for new, old, and remodel jobs and installed and removed many flush mount heaters; even surface mount and stand alone heaters over the past 30years and if this photo is of one of your heaters I believe you may already have a code violation. Your pipeage in the attic is correct for this heater even though someone ran "Galvanized" instead of the more affordable "Black" steel pipe. Your other picture shows the heater, but doesn't show any access door or panel to get in to the fittings to connect
(or disconnect) the gas line coming down the wall. I don't know about Louisiana, but here in Ills in noise state code requires free and open access to a gas cock on the end of your gas line. At that point there different interpretations how to terminate the line into the heater. One mandates that the gas cock be "hard-piped" with nipples,elbows, and a black union into the heater. This is definitely the safest route, but you can lose a few hairs trying to do it. The other way, and this depends on your building department codes, is to use a teflon coated stainless steel gas flexy. This is much simpler, but if ever there were a fire in the house, the 1/2" black pipe would still be intact long after the gas flexy vaporized. Either way put a 1/2" ball valve type gas cock on the end of your gas line (They do not leak) and when you do your remodel just put a 1/2" plug in the open end of the gas cock.
(or disconnect) the gas line coming down the wall. I don't know about Louisiana, but here in Ills in noise state code requires free and open access to a gas cock on the end of your gas line. At that point there different interpretations how to terminate the line into the heater. One mandates that the gas cock be "hard-piped" with nipples,elbows, and a black union into the heater. This is definitely the safest route, but you can lose a few hairs trying to do it. The other way, and this depends on your building department codes, is to use a teflon coated stainless steel gas flexy. This is much simpler, but if ever there were a fire in the house, the 1/2" black pipe would still be intact long after the gas flexy vaporized. Either way put a 1/2" ball valve type gas cock on the end of your gas line (They do not leak) and when you do your remodel just put a 1/2" plug in the open end of the gas cock.