Pro Football Talk's Josh Alper wrote that Dallas made the announcements Thursday afternoon. Demercado had been claimed off waivers from the Kansas City Chiefs ahead of Week 1. In two appearances with the Cowboys he ran five times for 15 yards. Alper also noted Demercado's recent Cardinals work: 131 carries for 834 yards and three touchdowns in 40 games over the last three seasons, plus 50 catches for 324 yards and a touchdown.
ESPN's Thursday transaction wire lists the same pair of moves: Smith activated from injured reserve, Demercado waived. Aaron Wilson posted the Cowboys' set of roster actions as well, including elevations of defensive backs Reddy Steward and Juanyeh Thomas for tonight. Those elevations do not add a running back.
For RSO owners, Demercado is off the Dallas active roster for Thursday night. Five carries in two games was already a reserve role, and a waiver ends it. Smith is a guard, so this does not install a new lead back. It only removes Demercado from the mix. Do not treat the cut as news about anyone else's workload unless Dallas says so.
Alper wrote that the same announcement elevated Reddy Steward and Juanyeh Thomas for the Buccaneers game. Both are defensive backs, so the only skill-position name leaving the active roster in this set is Demercado. Smith returns as a left guard. That is an offensive-line activation, not a new Dallas runner for Thursday night.
What to watch is whether another club claims Demercado. His Cardinals production is why a claim is plausible. If he clears, he can land on a practice squad, including Dallas's, but that is not a Thursday night role. Anyone who still had him in a Cowboys lineup should take him out before kickoff.