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