For the cheats part there is a tutorial on www.gaminw.net about them.
For the end score it sounds like you just need a variable that increases at specific points.Then when the game ends you do what bluecube said about resetting the variables,switches and everything.Then when you got tho the new game plus you program in your fork conditions so that if you got over 600 points in the last game you receive a Blue Sword.If you get over 700 points you get red sword and so on.Then you would reset that variable,or you could continue it so you could get 300 points in the first game,560 in the second.So 560+300+860,that way you could link the games so playing multiple times would be alot more beneficial.If you are having it that you get the items at the end of the game instead of at the beginning of the next
game,just program in the forks before the game ends.Then when you start the next game just be sure to not erase the items you received.