The Enage module is pretty non-inavasive, but it is true that one shouldn't add modules to a system without a proper backup and restore prodecure in place. So, if there is someone responsible for that aspect of the system then get them to back it up and install the module.
However, that fact that you're moving system folders around the portal indicates that you have full server access and should be able to do a backup and restore yourself. This is something that is vital when running an application like DNN. If you're worried about updating 100 image paths then you should be extremely worried about losing the entire system if something goes wrong, which it can at any time. Restoring from backup when something goes wrong is by far the best risk mitigation strategy in this. Backing up means both the file system and the database.
I would also definitiely advise updating the image paths in the actual modules rather than moving or duplicating system folders. The content management aspect of DNN should normally be done entirely via the DNN interface, never via the server file system or ftp. DNN keeps track of everything it does in its own database. One can remove or move files around the server and DNN won't know about it. Conversely, DNN can apply view and edit permissions on pages, files and folders without having to tell the server what it has done. When the initial server permissions are set, full control is handed over to the DNN portal. From then on, the portal should handle everything. Consider all folders and files that are not visible in the DNN file manager module to be permanent system items that should stay where they are.
You'll obviously know most or all of this, but I'm spelling it out anyways in case others are reading this at some point.
You're correct that the F3 module is not clear about the replacement aspect. In fact, it doesn't pop the replace option up until you've actually done the search. Then it provides a button to each module where the itme was found, or it lets you do them all at once. Be accurate with the replacement - Don't just search for "test/" and replace with "/". Instead, search for something more complete like "/test/portal/" and replace with "/portal/"
Let us know how you get on.
Rob