You're really making me think there.
Actually, I think "change trains" carries a hint of an elided prepositional phrase ("change from one train to another" or something). Similarly: "jump ship" = "jump off the ship"; "fled the room" = "fled out of the room".
While "change trains" and "jump ship" are idiomatic, "flee something" is more formulaic, since the noun phrases vary and take the article. If you google "fled the", you'll find most of the things you flee are places. There are notable exceptions:
"fled the violence", "fled the Nazis", ...
The question is whether the constructions above have a stronger sense of being surrounded than the versions "fled from the violence", "fled from the Nazis"... [Interestingly, my Oxford Dictionary of English calls the noun phrases in this case "objects", hehe, so perhaps I should treat this differently, on account of being less idiomatic and more prone to word-creativity.]
I do think that in all such constructions there's a predominant sense of location to the noun-phrases.
What I'm saying here is that I, instinctively, parse "change trains" as a single process before I think about participant roles. Rather than asking who's involved with "changing" and coming up with "We" and "trains", I'd ask who's involved with "changing trains" and come up with "we". "Change" alone can take that function. Could you explain the following point further?As far as participant roles are concerned, I'd ask who's involved with "changing trains". If the context takes care of "trains", you can just leave it off."Take the train for Brighton and change at East Croydon Station for East Grinstead then follow directions above."
You can't do that with complements as easily. You can of course elide complements:
"He's captain, now." - "Yeah, they appointed him yesterday."
But the lexical meaning of "appoint" doesn't change. On the other hand, the meaning of "change" and "change trains" appears to be the same. I do think that "trains" is implied in "change" rather than an deictic ellipsis. Actually, I think that "change trains" is the marked version of "change" (but I'd have to look at usage to be sure).
In summary, I think the term train relates more closely to the verb itself than to the verb's subject.
This is different from "She is upstairs," actually. (And now I can't resist poking the hornets nest...) To me, upstairs is more closely related to the subject than to the verb. ("Sally?" - "Upstairs.") I do think linking-to-be is merely a dummy verb; little more than a grammatical function. (See how the hornets come buzzing now? This is a discussion that involves various concepts such as "intransitive prepositions". I should leave things alone...)