The 25-year-old Boyle, who made 29 substitute appearances for his home-town club from 2006-09, had his first training session with the Tigers on Thursday and will go straight into the team to play Huddersfield on Saturday.
Both players have signed contracts with their new clubs to the end of next season after completing an exchange deal that suits both men.
"There's no hidden agenda," said Castleford coach Ian Millward. "Jake is a good young front rower and I wish him nothing but success in his career.
"It's a situation that suits both parties and both players. Ryan lives close to the ground and he's travelling to Salford, whereas Jake is from Lancashire and has quite a few mates playing at Salford.
"I like the way Ryan goes about his business. He's tough and we believe there is some improvement still there. He'll be a good addition for us.
"He's a Cas junior and I spoke to a few of the players who spoke highly of him as a person and were keen to get him on board."
Boyle, who made the last of his 71 appearances for the City Reds in their surprise 21-20 win over Huddersfield on Good Friday, jumped at the chance to return "home".
"I thought I'd never get a chance to play for my home-town club again," he said. "I'm happy to get this chance. It's a massive privilege.
"I feel I've come back a lot better player and that I've something to offer."