The "Callous Guards" card states:
Put this card in front of you. Action cards that alter the line may not be played. (This includes adding or discarding nobles.) You may discard this card at any time.
If a player has the "Callous Guards" card in front of him/her, can another player play the "After You..." card which states:
Put the noble at the front of the line into another player's score pile.
A couple of us could not agree whether the play was allowed or not. I'm on the "it's legal" side because putting the noble at the front of the line into another player's score pile is not "discarding" the noble. I understand "discarding" as removing the noble into the discard pile (i.e. no one gets points for a "discarded" noble).
Others argued that putting the noble into another player's score pile was "altering" the line.