If you're doing it from VB, you might be able to read (and write) the data directly. For files it's actually done via a Windows API; it's only folders that use something specific to Opus. Details are here:
The Opus-specific NTFS ADS data is used for labels as well as comments (and for labels, it's stored against both files and folders, unlike comments), so if you're writing the data that is something to be weary of, as replacing the whole thing could remove your labels (if you have any).