Where to put the code

At a BuddyPress website I have, I wish to have a system in place where for example:

Level 1 members can see and maintain their own profiles only. (No access to others profiles)
Level 2 members can see others profiles too.

I think the following page suggests a solution for the above:

http://www.s2member.com/forums/topic/uri-restriction-for-buddypress-profile

Can someone please guide me where to put the second bit of code (following code):

$displayed_username = str_replace("/members/", "", $_SERVER["REQUEST_URI);
$slash = strpos($displayed_username, "/");
$displayed_username = substr_replace($displayed_username, "", $slash);

If I put the above code in wp-content/plugins/s2member/includes/classes/ruris.inc.php my website goes blank white!!

Thank you very much

http://wordpress.org/extend/plugins/s2member/