I have a "noConn" (from basic lib) connected directly to an Instance terminal.
There is no wire in between the two objects, meaning that it won't take a "label" for changing the net name.
How can I rename that (internal) signal name in this case?
You can't, as far as I know. I think you simply have to drag the noConn a little so that you have a short wire between them, and then you can add a label.