Apparently most icon-replacement programs only change the icons in Explorer (and the file-open dialogs, which are really part of Explorer as well).
There is at least one tool that does work on Opus as well, though. A tool called Icon Packager was mentioned recently:
resource.dopus.com/viewtopic.php ... lder+icons
Opus uses a standard Windows API to get the icons. It seems that the patching programs are specifically targeting explorer.exe, rather than patching the whole operating system, which is why you need one like Icon Packager which can be told to target dopus.exe as well.