skimmed through the geneva convention and there is no such article protecting paratroopers. the convention mainly deals with medics, pows and treatment of neutrals or civilians. So this shooting of paratrooper thing is something of a NS myth, or maybe something commando PCs tell their troops to 'zhuang dan'
That makes paratroopers fair game, go ahead and mount that mg on its tripod and set 84 mm to airburst and fire away.
If you want to do your own research, heres the link, like i said i only skimmed through
http://www.asociety.com/geneva1.html