MAC1, MAC2, and MAC3 are tile changing commands with pretty sparse documentation.
Stumbled upon this while trying to create a trench digging chapter.
MAC1 - Swap out both the graphics and the tile properties.
MAC2 - Do the tile change, but only swap out the graphics. Tile properties are the same as the original tile.
MAC3 - Swap out both the graphics and the tile properties AND play the water sound effect heard in Night of Farewells.
With MAC2 I can walk over cliffs I’ve swapped in.
With MAC3 tiles have their expected properties.