I don't know if Paul is a replacement or not but that video is such bullshit it makes me doubt it.

Also what are the odds of finding a replacement who looks enough and sounds enough like Paul, is left handed, and is a talented musician who continued to write hit songs. There's another video I saw on YouTube where he just keeps strumming chords and singing to himself until he basically has the key pieces to Get Back. Pretty impressive for a body double.