Icon of Volume Mounted as Folder

Is it possible to make Opus display a personalized icon for a folder that is a mounted NTFS volume?

I tried changing the icon using "Shell's Folder Properties > Customize > Change Icon", but nothing happens.

By default, Opus asks the operating system for the icon, so anything which works with the rest of Windows should also work with Opus. You'd probably want to investigate that if you also want your custom icon to be the same outside of Opus (e.g. File Open dialogs).

If you only care about the icon in Opus, then you should be able to override it using a label assigned to the folder's path, and set to change file icons. ( Preferences / Favorites and Recent / Labels )