Forgive me if this has been answered, but I can't find a thread on it. As I work on my project, I often have new images to add, but I want to add them to specific image subfolders. When I have a bunch of new ones to add, I find that I have to delete the current folders, add the updated folder tree and reassign images to everything again. Either I can't figure out how to do add images to an existing file structure, or it can't be done.

All you do there is under Resources, click the sub-folder you want the images to go into and you will see it turn white. This means it is selected. Now just add your images and they will go into that folder. If an image is already there in a folder (under Resources), just selectively pick which new images you want to add instead of trying to add an entire folder as you cannot overwrite images that are already linked inside of the project unless you use the Replace File button.