In an interview with Rare Gamer, Rare lead engineer James Thomas was asked about how achievements are handled in the upcoming collection. "So the 360 games are as they currently are on the 360, nothing added or taken away," he explained. "The benefit of this is that you get to use your existing achievements to get a head start in unlocking the bonus content within Rare Replay. … Now some swift maths should then give you a hint as to how much Gamerscore is within the remaining games and it's fair to say we've pushed the boat out on that one and broken normal conventions."
Some may view this as a negative, as re-earning achievements can be part of the fun of playing these games. However, there are other benefits to this arrangement, as Thomas noted that save games stored in the cloud will transfer to the Rare Replay versions of games you've played on 360.
Thomas also had some good news about the version of Conker's Bad Fur Day included with Rare Replay. Rather than offer the Live & Reloaded Xbox remake, which censored numerous parts of the game, Rare Replay offers the original N64 game.
"We did have a good old think about which of the versions we'd prefer to use but as we're trying to tell the story of characters created at Rare we'd prefer to start any tail at the beginning," Thomas said. "We felt that the Xbox version altered a little too much, whereas Banjo and Tooie are both the XBLA versions as we felt that not only did they stick to the original but made them look exceptional at the same time."
This likely means that the game won't offer online multiplayer, though.