Renda is in his second stint with Cincinnati. He batted .222 in 16 games, including five starts, last month.
Selsky had two earlier stints with the Reds, going 3 for 10 in eight games. He had surgery to repair torn cartilage in his left knee a month ago.
Smith is in his second stint with the Reds this season. He pitched in 21 games with a 2-1 record and 5.19 ERA from May until Aug. 29.
The team announced the moves before Tuesday night's game against the New York Mets.