I’m currently drawing a blank in trying to find what you mean by
“make sure that the styles in the templates take precedence on those in the document.”
I take your point about the danger of setting myself for a trap in saving a .odt version. I’ll think about that. The opposing risk is forgetting to change a (probably small set) of text items that must be changed, such as the ISBN. Maybe I could manage that risk by marking such items with a comment with some marker text.
OTOH, I’d need to save a .docx for the epub and the mobi versions too, and they have more substantive changes that would need to be reapplied each time, so I think on balance a .odt version for each version would be less likely to lead to errors.
Ideally I could have a front and back section for each version of each book (since these are version specific, with different ISBN, links), saved as .odt, so that when using styles exclusively, copy and paste the large bulk of the text might be reliable instead of unusable.