What is the easiest way to change the appearance of the life meter (i.e. to change the hearts to instead look like something else)? Do you need to do anything in the Subscreen Editor.
Life Meter
you just need to replace the tiles that are on page 0 on the tile pages. I think there might be more info on the ZC Wiki.
I did that, yet the game still shows hearts. Even if I change the color of the hearts, it defaults back.
Depending on the Subscreen Editor/ Tileset, sprites used the tiles may not be on page 0. Try to scroll through the tile pages until you find a match.