With a little poking around, I think I have discovered how to do this... You should un-associate, and then the next time you open, you should be able to associate with a new app.
From the menu, choose App settings, and then select the app that is associated. Look down a bit and you will find a "Launch by Default" section with a "Clear Defaults" button.
I just tried this and cleared defaults for Chrome, and the next link I touched it had me choose an app...