Try this link: 
http://www.auran.com/TRS2004/DLS_downloadasset.php?DownloadID=40274
I have never used triggers to change the direction of a junction either, but believe it can be done.
Note that AI will automatically aligh a junction for a train after it comes to a full stop at the signal protecting the junction, if no train is approaching in the opposite direction.
Caution here: I believe AI will allow the train to proceed after stopping at the signal, even if there IS a train approaching at least two blocks away, since automatic or other type of signal will prevent the signal at the junction from detecting an occupied block after it can see two clear ones ahead.
There is a rule "Trigger Multiple Signals" you can use to trigger one signal by another's indication. I believe this rule will only put the "slave" or triggered signal into its most restricting position; stop.
So, you could control a signal at a junction using a trigger that is at an "automatic" signal two or more blocks away to prevent AI from allowing a train from getting a clear or anything other than stop when a train is approaching in the opposite direction beyond the next interlocking.
If you do not use automatic (or whatever you want to call a non-CTC signal) signals between interlockings (junctions), then you don't need to go through all of this.
Maybe I can experiment on my route with triggers controlling junctions. If so, I'll post a reply to this thread.
FW