On one occasion recently, however, I was called over as director. The dummy was something like:
The call was because declarer, leading from dummy, had said "The king of spades, sorry clubs"; this was clearly an attempt to change a designated card. Both opps agreed readily that there had been no pause for thought, and that the change of play was entirely OK by them, but had said "let's just call the director to be sure".
There's hope yet.