I want to automatically rewrite .html files

[cipric]

I want to automatically rewrite .html files in order to load each time a new file is required by browser a pop-up for instance, or to insert automatically a div in the header of the page and put some text inside that div so that a user requires that page can see that text.
Is there any way it can be done?

[treeline]

Use server side includes. SSI. Can insert all sorts of things this way.

[Storyman]

You might also want to investigate using PHP.