Updating 1,500 mp3 files ID3 tags based on filenames?

I have searched for a solution but I think the answer is "No" on this or at least "Not easily".

I have a heap of mp3s that have TERRIBLE ID3 tags but the filenames are generally pretty good (mostly as a result of many passes of cleanups using KM). So now I'm trying to work out how I can use the filename info to batch process the ID3 tags.

Is this do-able in any reasonable way at all (without having to use the Music app)?

There are many applications specifically designed for the curation of mp3 metadata, including updating them from music databases. While it is certainly possible working on these files with KM, I would have a look at e.g. Tagger, Mp3tag, Tag Editor for Mac first. Name Mangler and Better Rename should work with ID3 tags as well, but I am not sure if in the intended way.