Unfortunately, no. The closest Red Faction Guerilla has to a New Game Plus feature is that after the final battle you can return to the liberated zones and replay guerilla actions.
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As you have finished the game you can either complete the side missions or try out New Game Plus mode or Riddler's Revenge
all you have to do is start a new game and save on your new game file what is a new game file?
The Old game was made before the New game.
go to where you would load the game and simply hit new game