Not to burst your bubble but "piercing shot" is already in there as marksman's fang and ricochet basically fulfils "double shot"'s role. Headshot is basically covered by sniper which gives a double damage attack when using it from sneaking.
I'm not trying to be rude but please look through the wiki before making suggestions
http://divinityoriginalsin2.wiki.fextralife.com/Divinity+Original+Sin+2+Wiki
