Is there any log created by FreePBX that shows changes made to the system by administrators? Basically a sort of paper trail to show what changes administrators made and when they made the changes? Thanks
This is not something that FreePBX has at the moment.
But your /var/log/(apache2|http)/access(whatever)log will give you a clue about who went where and when.
In the FreePBX distro
less /var/log/httpd/access_log
(which if you read it will probably scare the little cotton socks off you if you don’t have a proper firewall in place 
)