This has become one of my favourite programs:
https://github.com/AlexanderPro/Smar...es/tag/v2.30.0
He just added a new menu item "Change Icon" (support of .ico, .bmp, .png, .gif, .jpg, .tiff, .wmf files).
I think this specific feature is not ready yet, though. It's taking too long to open the explorer dialog to choose the icon and only applies to current window state. Reflects on taskbar but doesn't save the setting across program restarts.