Genjikaz

Mod like this has been made several times, http://www.nexusmods.com/fallout4/mods/3605/? ^ this is the most popular one so far and is updated

Enhanced Blood Textures for Skyrim made the body spasm for a few seconds after death, but that was done with scripts. Right now we don't have access to proper scripting for Fallout 4 until the official mod tools come out, as far as I know anyway. Once the tools do come out I'm sure the author of Enhanced Blood Textures will do the same for FO4 as he did for Skyrim. I'm not sure making individual body parts move is a possible though, that's beyond me.