wow, I've searched all over, and I'm actually amazed...is there really no console command sequence that will change the Courier's Duster?

I was even willing to additem a new one and leave the old stashed at the canyon wreckage...is this seriously not possible??

Each one of them is a different item. So it is sort of like changing Veteran Ranger Armor into Riot Gear.

Why can't you add it? For future reference, there is a mod that will make the allegiance part a little more straightforward: http://newvegas.nexusmods.com/mods/44042