For anyone who is looking for a way to change the :uploads assigns to set the max_entries property, we can use Map.put to update the entire assigns socket on maybe_update_upload_config/2, something like this:

defp maybe_update_upload_config(socket, max_entries) do
    config = Map.get(socket.assigns.uploads, :images)
    new_uploads =
      Map.put(socket.assigns.uploads, :images, %{config | max_entries: max_entries})
    new_assign = Map.put(socket.assigns, :uploads, new_uploads)

    Map.put(socket, :assigns, new_assign)
  end