redirect all pages to index.php except one page

Hi hope someone can help me with this. This is not a plugin specific question

I like to temporarily redirect all links of my website to index.php I use the .htaccess below and it works

RewriteEngine On
RewriteCond %{HTTP_HOST} !^www\.
RewriteRule (.*) http://www.%{HTTP_HOST}/$1 [R=302,L]
RewriteRule \/.+ / [L,R]

How can I make an exemption to say to a file located at http://mydomain.com/exempted/page.html so that link will not redirect to the index.php

Thanks