In other words, can you update the spine tag with a script instead of converting to zip, opening, and replacing? Thanks.
Create an epub3 book or convert your existing epub2 book to an epub3 book and add a
page-progression-direction="rtl" attribute to the
<spine> tag in the
You can convert epub2 books to epub3 books with Calibre. (Polish books ▶ Upgrade book internals.)