Well, I would encourage someone to try it, as I know it used to be done sometimes. But only if they're seriously bored.

I took apart, or tried to take apart, two NR derailleurs, Davester. One came apart like a breeze. On the other, those pins wouldn't budge, no matter what I tried.
I even tried pushing them out using my 5 ton hydraulic press. No go. My experience echoes another member's here, OTIS. These can be a real pain. But I'm sure a mechanic better equipped or skilled than I am might succeed.

I still have one NOS pin, Davester. It measures at 3.48 mm. I never did figure out what material they used for the pins. Some say it was just aluminum bar stock. Maybe so. I tend to suspect it may have been another alloy, like possibly Zamak, (zinc, aluminum, magnesium, copper alloy) or something similar. Something a bit more malleable than aluminum. Don't know. I suspect they peened the ends of those pins using a big pneumatic press. Requiring special jigs and such to hold the part. I don't think that you could use the pins again, once removed from your spare derailleur, as removing them probably requires removing the "peened" end of the pin, on one end, in order to press or pound out the pins.

I've still got a few NOS NR derailleur parts here, including a couple of face plates. But now they just curiosities, for me.
I met my match trying to do this project.