I'm just now circling back to this. Thank you very much for the attempt to help, but I don't think this is working based on your instructions.
I moved the zip file (or more exactly, the .gz files) into the folder where the default skin was. I tried to unzip conventionally, but I got 3,000+ errors and no unzipped files. So I opened WinRAR and dragged the file out into the folder. I then renamed the original file there skin.bin.old. This is what that looks like in Windows Explorer:
Then I opened up OOTP. It went immediately to Classic Skin, I think because it does not see skin.bin in the folder.
When I tried to change to regular OOTP, the screen went black and the game froze. I had to open Task Manager to hard shut down the game.
It's a good thing I didn't delete the skin.bin file. It's a good thing I renamed it instead. Otherwise, I'd've lost that OOTP skin completely.
What am I doing wrong here?