Instead of trying to make page breaks undeletable, think about your document structure.
In your example, you cite a bibliography. A bibliography begin with a title and then the entries follow. The bibliography is a separate part in your document with its own presentation, header and footer, perhaps a different page numbering. This leads to design specific paragraph, character and page styles for the bibliography.
One important paragraph style is the one dedicated to the title. This paragraph style will contain THE page break to switch to the bibliography page style.
Now what is the risk? Your user can delete everything before the bibliography title without impact on it: the bibliography always starts on a new page… The bibliography merges with the preceding document part only if user erases bibliography title and its paragraph mark. Erasing the title is obviously something which is visible. It can be cancelled and reverted (
Z) or the title can be retyped AND the paragraph restyled to bibliography title.
The same holds for the other document parts: title page(s), TOC, chapters, indexes, … A template primarily contains reusable styles, so learn how to use them if you don’t know yet. Then design those to fit your needs, not neglecting the Next Style property which can provide automatic paragraph style transition thus speeding typing with fewer manual manipulations.
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