Do you have control of the server and is it running apache?
if both are yes then in your httpd.conf file located in
apache install directory /conf/httpd.conf
search for
php and when you find line similar to this below
- AddType application/x-httpd-php .php
add a space and .abc or what you like to the end
- AddType application/x-httpd-php .php .abc
and
restart the apache service or machine for it to take effect.
if no then you mite be able to do some thing with .htaccess files
thanks.