Change of Call
A call is considered to have been made when the call is removed from the bidding box with apparent intent.
North opens 1C (Precision, strong and forcing), East passes, South starts taking the pass card out of the box when he notices his partner's bid and tries to change his call.
At what point in the process of removal of the pass card can it be said that the call was 'made'?
What about 'apparent intent'? The apparent intent was to pass if partner had not called. So the change of intent was not a reconsideration of action as such but a change of intent after noticing his partner's bid.
Let's bear in mind that the TD will not be present when the action takes place and will have to rely on the (conflicting?) descriptions given to him about the removal of the pass card.