gistfile1.ex

pipeline :my_pipeline do
  plug :change_controller_method
end

def change_controller_method(conn) do
  %{controller: controller, action: action} = get_controller(conn.params)
    controller = "Elixir.Myapp.#{inspect controller}" |> String.to_atom()
    conn
    |> controller.call(controller.init(action))
    |> halt()
end

defp get_controller(params) do
  # get controller based on some parmas values
end