You used to have the majority files using an extension like .php and have changed everything to .htm so using a 301 redirect you can update all links to use the new extension.

All .php files redirect to .htm files, such as xpertphp.com/file.php to xpertphp.com/file.htm

Follow below example of All files with certain extension.


RewriteEngine On
RewriteCond %{REQUEST_URI} .php$
RewriteRule ^(.*).php$ /$1.htm [R=301,L]