I have multiple artboards using the same graphic/layer within each of the artboards.
Without using smart objects, is there a way to not only apply a layer style such as a Color Overlay onto those duplicated layers but to globally edit the layer styles as well? A script or plugin possibly?
You can record action what is not very difficult but... Actions have limitations, you can use action only in documents where layers/groups have exactly same names as when actions is recorded or you must have exactly same layer structure all the time.
I am not aware of script nor I am capable of writing one, please wait for script guys who may be able to help you.