I’ve had it done but not done it myself; with that said, I was a lube tech (pit bitch, grease monkey, whatever you want to call me) for 7 years and did diff fluid replacements hundreds of times on many many many 4x4 vehicles, and I’ve never heard of putting anything in neutral to service differentials on typical 4x4 setup. Can’t swear it isn’t correct on these Exploders, but in my experience it was always just a matter of dump out the old and fill with new. I believe both axles on these even have drain plugs so there’s no need to remove the covers or to suction the fluid out.
I haven’t seen the service manual for this model but that sounds more like a transmission service instruction and even then that sounds weird.