When I first read the question, my initial reaction to the answer was a resounding no. And it still is because of the legal, moral, and ethical aspects of the situation. However, I do think I have found one exception where I would shoot a deer that would be tagged by another or tag one that was shot my another. The only situation where I would do that is with a wounded deer that needed to be put down because it would not survive. And before that situation would happen, I would want verbal confirmation of what was about to happen so both parties knew and understood that this was being done.

Other than that specific instance however...no, I wouldn't tag a deer that someone else shot.