I am trying to create a document basically of one style but with a few scattered pages with a slight varient of that style.
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What do you mean with “one style” and “variant of that style”? Are you talking about a paragraph, character, page, frame or list style? These are the style categories Writer can handle.
Describe what you intent to do (as an author) rather than the solution you have in mind. You might be on the wrong track.
While you’re at it, mention your OS name and LO version.
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The purpose of the “manual page break” is that you can set another page style for the next page. Therefore, you can only select a page style in the list box in your question. No other styles are available there.
Please note that a page style is something completely different from a paragraph or character style. A character style will only have effect on selected text. A paragraph style will only have effect on selected text and the rest of the paragraph(s) containing the selection, but nothing else. A page style has effect on any number of “pages” in your document, and only stops when told to, by a manual page break, or some other way to change page styles.
Menu changes can be made from Tools/Customize
The Target drop-down list allows a specific menu item to be selected.
The Assigned Commands box shows what commands are available in a given menu item.
The list of Available Commands in the box to the left shows what commands are possible to add to it.
Hello,
create the new page style in advance and it will be available in the drop down at Insert -> More Breaks -> Manual Break... just as shown in the following screenshot (example here: MyNewVariantStyle)
How to create a new page style: LibreOffice Help - Creating and Applying Page Styles
Hope that helps.