I'm surprised that NOBODY over the years has ever made a save editor for this game. Well, now there is! NSMBDS SE can edit all 3 files in the game with the following options:
Life Count
Coin Count
Star Coins
Score
Mario/Luigi's current powerup
Inventory item
Bottom Screen BG
It can also unlock all the worlds in the game, as well as all the levels. (Be warned, as unlocking all the levels without unlocking the worlds first results in some small weird things that occur on the worldmap!)
How...
New Super Mario Bros. Save Editor Tool
Life Count
Coin Count
Star Coins
Score
Mario/Luigi's current powerup
Inventory item
Bottom Screen BG
It can also unlock all the worlds in the game, as well as all the levels. (Be warned, as unlocking all the levels without unlocking the worlds first results in some small weird things that occur on the worldmap!)
How...
New Super Mario Bros. Save Editor Tool