How do you edit a line shape on pages template

I'm trying to create a custom template for pages starting with an existing one. I'm starting with the invoice template but would like to change the horizontal lines that appear at the top and bottom of the page. No matter what I do, I can't seem to select those lines. I seem to be able to select anything else on the page but not those lines. I've tried saving as a new template and reopening but they still aren't selectable. It seems the point of a template is to provide a starting point rather than giving you an exact form so I would think this should be doable. How do I edit line shapes that are part of a pages template so that I can modify or delete them? Thanks.