Ah, yes I’m trying to open a saved level from the menu level.
So at the start of the game, it loads a menu level that displays a menu widget.
Here you can select a saved game that opens one of the worlds that the game was saved in.
(I hope this is explaining it correctly) 
It doesn’t look like the Save Extension is using object IDs but that is something I’m still searching for in their documents. But I know that it doesn’t save the game mode.
(here is a link: Piperift - Save Extension)