As Peter said, you could save the menu into a template page if the menu is going to be in the same location on every page and apply the template to the other pages, or you could save the menu contents and theme as presets when you make modifications to them. After clicking ok in the edit menu structure/theme windows, a popup should appear to ask you if you would like to save as a preset. In this case you can save as preset and then on your other pages you can apply the same menu by choosing the presets that you saved for structure and theme.