Hi again...
Can't quite see why you actually WANT a swap command really, but it is a complete doddle to do should you insist on it

I'm assuming at some point you want to make 'object b' replace 'object a' in the current location. Assuming both already exist and item b is in some limbo room the player never sees you'd use the following ASL:
move <object a;#name_of_limbo_room#>
move <object b;#quest.currentroom#>
You could make it a procedure if you wanted, but it is such a minor piece of code it seems hardly worth the bother...
Al (MaDbRiT)