Seriously, is there a way to edit where the trams go after unloading?
As explained many times already on the forum, the only thing GSX knows about the outside world is the AFCAD. Since there's no such thing as a "terminal" in the AFCAD, the only place when things can appear or disappear, is a parking.
If the scenery is accurate, and the designer included a proper vehicle parking, they appear/disappear there, by preference but, if there's none, they'll use a regular parking.