Is it possible if someone could remodel the allied rifle grenade to have a pin to the top, and then make it so that whenever a new rifle grenade is mounted on the rifle (reloaded, basically), the pin is pulled? A lot like in the movie Flags of our Fathers.

I get what you're saying, but I think the animation where the rifle grenades are put on/put in is too quick to have something like that added on, or even noticeable.