Is there code to manually update the Places and Objects list?

I don't really understand what you mean......

Do you mean edit the objects/goto exits without using QDK?

no i think he means, if list list changes, it tells you type thing....

I mean the actual "Places and Objects:" window pane in the Quest GUI.

It seems to blink (update) when other players are moving around in a QuestNet game so I have some sneaky code in mind to take advantage of that.

The question arose when I had an NPC wandering in and out of a room and he was still listed in the "Places and Objects" window after he had left.

just use the hiding thing, in QDK, under the object menu....

To answer my own question:
Yes. For singleplayer, all you have to do is hide an object. For multiplayer, hide an object in the context of the player whose window will be updated. If you don't want to use a dummy object then hide any object then unhide it. The object does not have to be available or in the same room.