Super Mario Bros 3 hackers now have a stable and relatively easy method of creating alternate paths and secret exits to different paths in their overworld maps, with the help of this document.

Using unused pipe-sets in the game, the maker will simply place a certain enemy object to a certain set of coordinates at the beginning of a level to make the player return to the overworld map to the maker’s desired location upon completing the level.

See Document for all relevant details on fulfilling this method.