Chapas was one of the Cowboys' two seventh-round picks in April. He had two carries for five yards and two catches for 20 yards in the preseason before he was released.
He has spent the entire season on the practice squad.
Fiammetta has missed the past two games with an undisclosed illness that cropped up following the Cowboys' win against Buffalo. He has undergone a series of tests to determine his ailment.
Fiammetta has played a big part in the Cowboys' running game. With him, the Cowboys average 145.8 yards a game on the ground and 5.6 yards per carry. Without him, they have averaged 85.6 yards and 3.2 per carry.
The Cowboys have used their tight ends, mostly John Phillips, as the lead blocker in Fiammetta's absence. Chapas, who also can contribute on special teams, has the more natural feel for the position even if he lacks NFL game experience.
Chapas started 22 of 49 games at Georgia and finished with 40 carries for 155 yards and three touchdowns, while catching 26 passes for 221 yards and four touchdowns.
Owusu-Ansah, who averaged 7.8 yards per punt return and 18.7 yards on kickoffs, is eligible for the practice squad if he clears waivers.
The Cowboys also added running back Chauncey Washington to the practice squad.
Washington spent parts of the 2009 season with the Cowboys before joining the New York Jets and St. Louis Rams. He was cut by the Rams in training camp this summer. He played in two games on special teams for the Cowboys and did not have a carry.
The Cowboys were in need of a tailback because Phillip Tanner is bothered by a hamstring strain. Tanner has been mostly a special teams' contributor (three tackles) but has 22 carries for 76 yards and a touchdown this season. He has also caught two passes for 11 yards.
Todd Archer covers the Cowboys for ESPNDallas.com.