When you're selecting teams in Play Now Mode, you'll see an option in the middle that by default will read "Current Game", indicating that the game will use your current DNA data. You can toggle this option to previous NBA Live Rewind games that are available for the currently selected teams; on the Xbox 360, you use the left and right bumpers, on the PS3 I believe it's R1 and L1.
does the nba live rewind really have it play by play or by end score only? do they have now the rewinds for the finals between lakers and celtics? if there is, does the court have the "finals" logo?
NBA Live Rewind loads the DNA and roster data from the game in question and also allows you to look at the boxscores. It doesn't modify any of the aesthetics like courts, player hairstyles etc.