We played this game last night at my games club and the use of the "Coup" card was questioned.
The question was this: If (for example) hearts are led and say the Jack, Queen and Ten are played and it gets to the fourth person who has a Seven of Hearts and the Coup Card in their hand.......can they choose to play the Coup card to win the trick, or do they have to play the heart?
The rules just say that the Coup card is wild and it is the highest card. One person thought it would count as being from any suit (i.e. wild) while another felt that it could only be played when there were no cards left in suit being led.
In the past, we had always played that it was the highest card in the suit being led and that it could be played at anytime, so this was a "new" question for me.
My interpretation of the rules is the same as yours: it can be played at any time and declared to be any value. This would typically be the ace of the suit led so the coup player can take the trick. There is nothing in the rules stating that the Coup card can't be played if the Coup player has other cards of the led suit. (The rules only state that it won't beat an ace if the ace was played first.)