Hanson, an eighth-year pro who made 31 tackles and one interception last season, was let go during last weekend's final roster cutdown.
"(We thought) keeping another veteran player would work out," Reid said. "(General manager) Howie (Roseman) and I decided as time went on to bring him back."
Smith, who was signed away from the NFC East rival New York Giants, has been practicing in a rotation with the starters, Reid said, adding that the receiver, who had microfracture surgery, could play Sunday as well.
Maclin, 23, caught 70 passes for 964 yards and 10 touchdowns last season and has 125 receptions for 1,726 yards and 14 scores in two NFL seasons. He has missed only one game as a pro. A sore foot kept him out of a game against the San Francisco 49ers during his rookie year.
"Sometimes it's good to take one small step back to take a big step forward," said Reid, who wouldn't confirm the move at his press conference. Reid said Watkins "will be out there practicing. We got Kyle, who also can play, in that spot. We're comfortable with either direction that we go."