By coincidence, there is just the wiki for what you're asking!
https://github.com/rogerwang/node-webkit/wiki/Icons
I believe also Windows caches app icons. So if it doesn't "work" visually right away, then keep in mind if you forward the files off to a new computer it should reflect all your changes.
Edit: in other words, if you have a friend available, ship 'em your files to make sure they're to your liking.
Thank you for the information.