I cannot find the rules on precisely who gets to 'swap weapons' -- thanks.

The rules for swapping weapons are in the chapter "weapons and gear" just before the section about special strikes.

It will cost you 1 point for an warrior, but you can swap a sword or a dagger for an axe f.i.

I'm not sure, if it is allowed, to swap just one sword of the Karna twin blades. These seem to be thought as a unique weapons combination, which should not be splitted.

But in the case of a watcher with a bow and a dagger I don't see a problem in swapping the dagger for another hand weapon, a single handed one of course.

The Armybuilder by LK does not have a 'swap weapons' option for Watchers of Karna. I am away from my books just now, but will look into this 'unique weapons' thing. Anything I have missed?

Sorry, bruceqn, this "unique weapon" thought is just my opinion, you will not find it in the rulebook.

But on the strictly fomal side, "twin blades" are not listed as weapons, that can be swapped. But of course, one can argue, that twin blade are hjust two swords, and a sword is swappable.

So, sorry again, I cannot really rely on a certain rule from the MESBG-books.

Anyway, its an interesting question, maybe it will become an entry in the FAQ by GW.