Well, if you open that rhino file again, it should have the sender stored. You can then add/remove/modify objects from the sender using the super intuitive speckleUi™.
Existing sent objects are tracked, and if you change them in any way, the stream will update!
Speckle doesn’t allow (yet) modifying senders from multiple locations/sources. So if you want to modify an existing stream in a new place/file, just bake the contents from a receiver and make a new sender.