Can there be any downside of this setup?
I wish to have the ability to run PHP5 filters and processes... Will renaming personal files to something.php5 let me do that?
My host company recommended this rather than improving to PHP5. The default continues to be php4 with registered_globals ON
Altering the file extensions will not alter the version of PHP that's placed on the server. In case your host has only PHP4 you'll be able to just use PHP4 unless of course they are willing to provide you with PHP5. The only method this works is that if your host already has PHP5 running and it has it setup to simply use files which have the .php5 extension (it is really an possible scenario).
I'd the first factor to complete is to produce a simple phpinfo file, like below, and title it using the .php5 extension and find out what it really states.
<?php phpinfo() ?>
phpinfo() provides you with the PHP version in large bold text towards the top of the file. Therefore if personal files with .php states it's PHP 4.x along with a .php5 file states its PHP 5.x, your host has both placed on the server and it is telling Apache to make use of PHP5 with .php5 files and PHP4 with .php files.
As well as on a side note in case your host has register_globals switched on plus they will not turn them off, I'd recommend putting the next inside a .htaccess file at the document root.
php_flag register_globals off
Are you currently permitted to rewrite individuals configurations per directory having a .htaccess file?
If you're able to, just request you host company the way the setting is created and alter it simply for you personally. Something similar to
Action application/x-httpd-php /path/to/php5