Linking Layers [How to link layers within different folders so I only have to update one image?]

Linked layers in Photoshop is a way of connecting layers to make them move as a group and to apply layer effects to as a group. What it sounds like what you want is to have identical layers that update both when either is changed. You can do this by making one of the layers a Smart Object and then duplicating that layer and placing it in the other group. Any Smart Object will update all of it's duplicates when changed (there is no parent/child relationship). To make a layer or group of layers into a Smart Object, select the layer or layers, right-click and select Convert to Smart Object. A Smart Object is essentially a Photoshop file inside the Photoshop file. To edit the Smart Object, double click on it's layers thumbnail in the Layers Panel, it will open as a separate file in Photoshop. Make any changes you want and Save and close the file. The changes made to it will be reflected in the Smart Object in the original file.