Thanks, I have managed to get it working with that :)
But is there any way for me to change GMRoomPack to just return IDs? I imagine it uses quite a bit more ram to save all that data, which I don't need. Perhaps it's negligible, but the game has thousands of instances loading in, so it might still make a meaningful difference.
It does not use more RAM, these are references to structs that already exist inside instances. That’s how GML works now.
You can find these two lines in GMRoomPack’s GML file
var l_list = room_pack_raw_store_instances;
if (l_list != undefined) ds_list_add(l_list, self);
and change the second line to use id instead of self, but I do not think you’ll win anything whatsoever in doing so.