control surface dissociation

If i map a midi control surface to a parameter (eg track fader or pan) using the Ctrl - middle-mouse-button - move-slider-on-control-surface procedure, how do i then go about ‘undoing’ this connection?

For example, if a set the first slider on my control surface to control the master fader in ardour, but then subsequently decide i want it to control the fader for track 1 instead, how would i do this?

repeating the Ctrl-click-slide procedure just adds another association, so moving the slider on the control surface controls both faders.

At the moment i’m having to save the project, exit ardour, and edit the .ardour file to remove the connections in the section of in order to get rid of the first association.