So if a president can award a pardon, can another President take it back?
A most interesting question.
If the pardon was issued after a trial, probably not. Doing so would be subjecting a person to double jeopardy.
But more interesting is the question of can a future President reverse a pre-emptive pardon. In that case the person pardoned was never subjected to any jeopardy in the first place, so there answer might be yes.
Especially if a very high degree of malfeasance comes to light after the pre-emptive pardon.
Also, note that Ford's pardon of Nixon was only for crimes against the United States, i.e. federal crimes. He could have still been charged with crimes against an individual state.