[KevinH]

As script tags do exist outside of head and inline scripts are possible in both head and body, linking and unlinking javascripts can not account for these, so there really is no way to just add or remove script manifest properties without parsing the entire xhtml file. And it would have to do that for each and every xhtml file.

Normally, a user should run that update manifest properties tool only once as the very last thing before the final save or epubcheck when editing an epub3. To do so earlier really does not accomplish anything as nothing in Sigil itself requires those properties to actually function.

Running it multiple times seems to be a waste.

What is the use case that requires it immediately after linking or unlinking javascript files and not just once before the final save as is needed/expected now? It is not required for Preview to run any javascripts.