before installation, you need to use your ftp program or the file manager of your control panel and change permissions on configuration.php to 777. Once you do that you'll be able to change the other settings through the admin panel of Joomla to make them available.
Just remember to change permissions back to unwriteable when you are done configuring your installation to what you want.
Oh, and the rg_emulation... leave it on, too, until you're done installing your extra components and mods. It's another vulnerability if it's left on but sometimes it needs to be on for some mods to install properly.