There's any way to unlock the full size of the stage without playing the in-game missions? I would like to know if there's any way to modify the user files and do that.

I know Score Attack also unlocks mission items


As far as a tool to edit the game files im not sure that has been/can be done



As a person with a corrupted save file (twice(dont put cdlc folders in your dlc)) I know how hard it is to grind to get all of the items in game.

I think easy med, and hard all unlock a mission item, so in theory, there can exist 1, 2, 3, 4 ,5, etc. note cdlc to unlock everything