How can I put TOC entry formats into my template?

I have a template for a collection of documents where I define various styles, in such a way that I can modify the template, and it will apply the change to all the documents that use the template. But I can’t seem to do this with TOC entries. I can only modify the TOC entry format in an actual TOC in a document, not in the template.
Am I missing something?

As you may have noticed, when you open a document based on a modified template, the dialog asks you whether you want to update styles. The automatic update involves only styles.

If you template contains changed fixed text, this content is not transferred to the derived document.

I tried to put dummy headings and the corresponding TOC in the template (not important because the TOC is regenerated with actual headings) and changed the structure. Unfortunately, this is not a style definition and is managed the same as fixed text. I think this is why it does not work.

Gurus familiar with the source code are kindly asked to confirm this.