I have this weird problem. I have an icon in my C++ project's resource section, and it tells me it's "res\icon123.ico". I make some changes to this icon and save/rebuild... and while the resource editor shows the new version, the .ico file in Explorer has not changed.
How is VS storing my changes and why won't it let me do what I want?
Individual .ico files can contain multiple copies of the icon, in different resolutions and color depths. You are probably editing one, while Explorer is showing a different one. Look for the resolution selection dropdown in Visual Studio to change which resolution you're editing.
I've had the same problem, and it has nothing to do with different icon formats in the file - you can entirely replace the .ico file and you'll still have this problem. My solution was to completely remove all the extra files built by Visual Studio like the .aps and .suo files. I'm not exactly sure which one caches the icon.