If you are looking to overwrite a file on disk, read perldoc perlopentut for info on specific use of the open() command.

If you are looking for specific commands within HTTP/HTML to use for these techniques, I'd recommend the information at Web Developers VL as a good jump-off point.

You can add a <meta http-equiv="refresh" content="###seconds;URL=next_page.html"> tag to your header to indicate a refresh to the browser (this is not reliable so include a link to the next page as well. Other than this, once you've sent the page... short of adding Java/Javascript to your page (or some other client-side technique), there is no way I know of to change a web page once it leaves your server.