There is going to be a problem with trying to have a single connection file for all of the pages in your setup. The problem is that the pages that were created with the existing connection will reference that connections name in the code for the recordsets and other db manipulation. The connection for PowerCMS is called localhost, so if your existing connection does not have the same name it will not work to have a single connection for the pages without updating your existing pages to work with the new connection file.
So you can either leave your connection file in place and have the PowerCMS connection file in its folder or you can update the require once line for your connection file and the connection name on your existing pages to use the new PowerCMS connection.
To update your existing pages you would update the require once to go into the CMS100 folder and then into Connections/localhost.php. You would also need to update the code on the page, you will need to look for the connection variable and update it to be the new $localhost value.