Direct formatting is a mystery land. It is not your friend at all and always plays tricks on your back. Newbies think it is “intuitive” because Word has no other way to do many things but DF occurs at many levels in ODF encoding. So you are never sure which layer Find & Replace
will hit.
The only safe and reliable way to format a document is through styles and only styles. Don’t direct format anything. Contrary to common sense, direct formatting requires guru skills to get it right. So learn styles and practice. This is your life jacket in the tempest-prone ocean of formatting.
Even if your document is huge, it looks like you’re trying to “maintain” it (making sure it can be read by newer versions of Writer, perhaps having it portable between suites, editing it, amending it, …), styling it is worth the trouble. By experience, you need ~10 user paragraph styles + Heading n family, ~10 character styles and a small handful of page styles. If you have lists, consider creating your list styles (or generally customising at most 2 built-in styles is enough) instead of relying on Format
>Bullets & Numbering
which another kind of hidden direct formatting (and very very nasty on you). And with pictures or other “inserts”, go for frame styles (2-3 are enough).
The more you style the document, the more you automate it and it becomes more and more resilient against editing (which can mode unexpectedly whole bunches of text and images).