not much is known about Reworks, except the fact that they are zombies working for Hell's army owned by Kane, aniway by some hints it seems that Reworks are distinguished in two categories:
1)the ones which are corpses of dead people, this corpses are sent to Hell and then turned into zombies by some strange creature, which resembles a lot the one seen in "Rework the dead", like for example Bonavin, which died and then his corpse was turned into a Rework, as suggested by Jack who says "this is just a husk, his souls has fled a long time ago", hinting that Bonavin's souls it's in Purgatory/Heaven but his corpse was turned into a Rework.
2) the ones who signed a pact to be turned into Reworks, this ones are souls who are sent to hell and then turned into Reworks by the same creature, this is seen in the arc "Those that run" where some souls signed a pact to escape Jack, but if they were captured they would be judged, and if sent to Hell, turned into Reworks, at the end all the souls are captured and turned into Reworks, except for a few who helped Jack, so they were sent to Purgatory.