Technically speaking, it should work fine also on the mac.
If you open the zip, you will see that applying the incest path in practical terms means just replacing some files that are in the "game" directory inside the game folder, and those files, are just the source code and its Ren'py compiled version.
It is just that I don't know how Ren'py "packages" the game, so I don't know if there is the same folder structure or not.
If there is the same folder structure, just follow the same instructions are for Windows.
If the game comes as a "monolithic" .app file, in general it really means inside the .app file there is actually a structure, you can try to do the modification by going inside the .app file and changing the files there.
I do not play "Myriam" on Mac (and right now, I do not have a Mac at hand, and the one I have, does not have the latest OS).