Currently, the use of "straight" html heading tags...
<h2>Chapter Heading 4</h2>
... already differs from the typical wiki mark-up's usage...
== Chapter Heading 4 ==
... in that the  link is not generated to the right of the headline text.
Unfortunately, the straight html element tag approach still causes each heading to become part of the built-in Table of Contents listing whether applicable or not.
Hoping there is a way to have the parser skip the creation of the span element involved with subsequent ToC listing if some condition was met beforehand (such as the presence of a class name under the heading tag for example)
<h2 class="mw-legacy">Chapter Heading 4</h2>
Doesn't matter if the class is added by Linker.php(?) or if user's must add it themselves; whatever is easier.
See more details at: https://test2.wikipedia.org/wiki/Headings