Smart Objects are your friend! They give you unlimited design possibilities and you can edit them forever--and any time you want. Picture a refrigerator that takes its own inventory. You can look at the picture on the door of the fridge and see exactly what's inside without having to open it. However, if open the door and put in more food, or use some up, the fridge immediately updates the list or picture of what's inside. That's essentially what a Smart Object does. It lets you use whatever is inside of it as if it were a single image. Even better, you need to OPEN the Smart Object in order to make a change; you can't do it 'by accident' in your file. If you resize your image, the Smart Object keeps its original size. If you cut off your image and only one pixel is left, you can restore the image from inside of the Smart Object and always get it back.
You can add images to the open Smart Object file and make non-destructive changes (you can make destructive ones too, but I hope you won't). In this video, I'll show you some of the things you can do. The secret is that you COPIED the first Smart Object into the other three Smart Object layers. Updating one Smart Object updates them all. For this to work, you need to have used the Layer > New > Layer via Copy command (COMMAND or CTRL +J). The Layer > Smart Objects > New Smart Object via Copy won't work here; it creates unlinked objects.
So, please enjoy the video. Ask my any questions if you have them.
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--Sherry (a.k.a the prancingpixel)