I´ve seen another homepage, (with MySQL) where the admin can edit HTML code in a textbox, and click on a button to save the changes. Can you do that without a MySQL database? see http://193.10.76.36/glc2/uppdatera_sida.php3?visa=1 (in swedish, but you may understand what I want)
Ofcourse you can. fopen to read the file, print it to a textarea in a form, and fopen to write the file when it is submitted.