It seems that the only way for me to give a user the ability to change renderers in Web AppBuilder or Ops Dashboard is to add the same layer multiple times symbolized different ways. It would be useful to allow users to view the same data, but rendered based on different attributes or as a heat map, or clustered and to give them the control to toggle between renderers defined in the Web Map or in the app. In Web AppBuilder you end up with the added complication that if you add the same layer rendered a different way but as multiple map layers, you can only set the Filter Widget to filter one of those layers. So being able to add the layer once with different rendering options would solve than issue as well.
