Before being re-signed to a practice squad, a player must clear waivers (this is where I think someone would grab Pryor ... low salary and no risk if it doesn't work out).
Once on a practice squad, a player can be signed by another team at any time. He's essentially a full-time free agent. The only condition is that the team that signs a player off another team's practice squad must keep him on the 53-man roster for the remainder of that season.
Hope that helps.