Hi,
If a link is clicked, TW sends a tm-navigate message, which is catched by the navigator widget.
There is a link-catcher widget, which will allow you to do a different thing instead using action widget.
If you would be more concrete, what you try to achieve we could probably point you in the exact direction.
Especially, if you want to control clicks in the story-river or if you want to change links in the sidebar. There is a big difference, where to place your changes.
have fun!
-mario