I would suggest that instead of trying to reference an object directly in another streamed level, which is an inherently brittle thing to do, consider using an event dispatcher or a [blueprint interface to implement a function that does what you want it to do.
So instead of trying to manipulate the objects directly in the streamed level, you throw an event or call a function, and then the level blueprint that contains the objects does what you need it to do with them. In the long run, this is going to be safer and less-prone to breakage than trying to reference objects across levels.