Using a sitemap as a template is quite easy. The best way to do so is opening a previously used sitemap that you want to use as the template. Once opened, just click File > Save > Save As and save the file as a new project name.
Doing this before editing it will make changes to the new sitemap without affecting the original. After you have saved it as a new file name, it never hurts to go back to dashboard so you can see both files, just in case. Alternatively, you can export and import XML files. To do so, check out our other article: How do I export my sitemaps?.