To do this would likely be an undertaking. You don't just change a few files and this works. You don't consider that a version of an entire engine is likely quite different from the previous versions. He couldn't simply transfer things, he'd need to go through most of the engine by hand, make sure his stuff still is compatible, make sure there aren't new things that might ruin the game, and all that.
Or, you could hire him a team to do it.
Edit: Damn you, blitz, and your interrupting posts.