itch.io

Yes indeed, unfortunately browsers (rightfully) stopped loading javascript from local HTML because of security implications. So you can't play it that way. There are browser plugins which allow local JS, but I do not recommend using them.
I'm looking into creating a desktop app to download, but this may take a bit.

Edit: I overlooked that you wanted to mod the game, so a desktop app won't help you. IMO the best thing you can do is to invest the time to install nodejs and learn to work with the source code of the game. It is available at https://github.com/ffalt/mah, otherwise your skin won't survive any game update.

After unpacking the zip you can open the file "index.html" with a browser.
This game is a website app which you can also start locally on your computer without internet.