Perversely, the author starts off getting this part wrong!
The correct answer here is to adopt the same mindset used for print, which is to say, "just don't worry about it; the value of doing so is oversold". If a print org changed their layout sometime between 1995 and 2005, did they issue a recall for all extant copies and then run around trying to replace them with ones consistent with the new "visual refresh"? If an error is noticed in print, it's handled by correcting it and issuing another edition.
As Tschichold says of the form of the book (in The Form of the Book):
The work of a book designer differs essentially from that of a graphic
artist. While the latter is constantly searching for new means of
expression, driven at the very least by his desire for a "personal style", a
book designer has to be the loyal and tactful servant of the written word.
It is his job to create a manner of presentation whose form neither
overshadows nor patronizes the content [... whereas] work of the graphic artist must
correspond to the needs of the day
The fact that people publishing to the web regularly do otherwise—and are expected to do otherwise—is a social problem that has nothing to do with the Web standards themselves. In fact, it has been widely lamented for a long time that with the figurative death of HTML frames, you can no longer update something in one place and have it spread to the entire experience using plain ol' HTML without resorting to a templating engine. It's only recently (with Web Components, etc.) that this has begun to change. (You can update the style and achieve consistency on a static site without the use of a static site generator—where every asset can be handcrafted, without a templating engine.) But it shouldn't need to change; the fixity is a strength.
As Tschichold goes on to say of the "perfect" design of the book, "methods and rules upon which it is impossible to improve have been developed over centuries". Creators publishing on the web would do well to observe, understand, and work similarly.
