And Thank You for (once again) noticing my work. 
As I had teased back then, this is one of the projects I had in development. My main concern was if the use of [CurrentPreview] in a manner outside of its scope could have unforeseen negative impacts elsewhere in Mp3Tag's internal workings, and was hesitant to release the script due to this (and lack of quality development time).
That is unfortunate. I had tested using [CurrentUrl] in an earlier draft, but since that data is essential to proper script operation, modifying it could cause the CAA API to reject the request (it had on other projects / APIs); so I tentatively went with [CurrentPreview], and its possible negative impacts.
Thank you for the input; I'll update the first post with this info.
But... here's some food for thought:
The addition of a %_CurrentClipboard% variable in [ParserIndex] could serve the same purpose, and would enable the script to run in macOS. I had sent you (at the time of the quoted post) some notes on this via PM, but just as it took me until now to properly debug and tidy up this script, I'm aware that you are also very busy with development to properly analyze and reply to every idea and suggestion that arrives to your inbox, and know better than to expect a reply straight away.
Oh, and one more thing.
You may have noticed that, in the initial query results, the cover preview thumbnail \ popup has its aspect ratio changed into squared dimensions. For square-ish physical cover art this isn't much of an issue, but for booklets, obi, and other 'less squared' images, there is a visual impact on the preview (see example). The end result (with "Correct aspect ratio" enabled) is fine, so I'll leave to your consideration if this is worth addressing.
Thank you once again. 