Cheat: JJCP, "-test" is activator, make it so that you can save in singleplayer (because the game will tell you that you can't save in singleplayer mode) and a custom command where you can set your rank experience by an amount, "-setrank ####" where as # is the amount.
Rank: Okay so you got a leaderboard on the top right of the screen where the amount of experience is located, it will gradually increased overtime and you have to save it by using the command: "-save". Later you can load it up by using "-load". The amount of the experience will increased if you kill enemies and completed objectives like missions.
like that.
EDIT: if not possible to do that then you can just add the JJCP and the singleplayer save.
