Depends what type of Pages document you are working with. As yours is a Word Processing document, content added below the existing content should not affect the position or spacing of the content above the insertion.
But if you add content in or above the existing content, the new content will require space, and will push the content below it further down the document. IF that results in the existing content being pushed precisely one page, two pages or n pages down AND all objects below the inserted content have been set to 'move with text,' the spacing within the shifted block of text should be unchanged.
If your document was a Page Layout document, each page would also be a separate section of the document. New pages are not automatically created when needed in PL document.
Placing new content without disturbing the position of existing content in relation to other content on the same page requires inserting a new Page/Section and adding the new content to that new page.
Regards,
Barry