Thanks for the info! Works like a charm for the .exe. I just couldn't change the titlebar icon...
Anyway, thanks for your help!
Just for reference, I found a way to change the NWJS window icon. Searching for the package.json in the C2 installation directory (which I assumed was the template which configs in NWJS are compiled from), eg C:\Program Files\Construct 2\exporters\html5\nwjs, opening up package.json revealed a property -> "icon": "icon-128.png". This "icon-128.png" is a reference to the current C2 project's /Icons folder. Editing this icon will change the window icon during export.
Alternately, you might be able to change the package.json template, but I think editing the C2 icon is better.