Hello Jersey,
The pin is nothing special. Just find a nail that's the right size for the hole. Not too tight, not too loose. I know, duh.
The toughest part of removing or replacing the pin is getting the panel pressed in enough to have access to the shaft. Another pair of hands helps out. They press the panel in, while you strategically with finesse of a surgeon and the mouth of a sailor, remove the pin. For pin removal, try using a coat hanger wire. You bend it to the angle you need. If the panel is pushed in enough, and no load on the shaft/pin, then the pin should push out easy. If not, use a small bent needle nose pliers to pull it out the rest of the way.
Here's two ways I've found that seem to work to replace the pins.
1. File a V in the nail where you want it to break off to the length you want.
Push the nail in, then snap it off at the V.
2. Use a nail with a flat head. File the head diameter down just enough so it will not push through the hole. (Don't use a finishing nail, for the head adds length, where the flat head doesn't.) Once nail has been cut to the right length, use the small bent needle nose pliers to hold the pin for insertion. The advantage of having a head is it will stop it from sliding through the shaft and dropping out.
Sounds good on paper, huh?!
I've removed the door panels more times than I'd like to admit. With practice, it's gets faster and easier.
Although I still do give the door panels the Deer In The Headlights Look, when I realize I need to remove it.
Cheers and good luck.
Roger