Thereafter, you could refer to it in an html region like so:
(You can also alternate this with the +&WORKSPACE_IMAGES.+ equivalent in certain circumstances)
<a href="#WORKSPACE_IMAGES#mygroovyfile.txt">download my file</a>
It sounds to me like you want to amend the page template, rather than the individual pages themselves. If you go into the 'Shared Components' section of your application and click on the 'templates' link, you will be presented with the various templates used in your application. You are mainly interested in the Page Templates here.
Once you are happy with the changes, just refer your new template in the page (or even change your default page template accordingly) and try the page again.