Right click on the Smart Object Layer you want to edit Edit Contents.
When new .psd file opens, paste your design.
After you are finished Save and close .psd window.
Those changes will be reflected upon returning to your main psd file.
Tips
White and black labels at separate layers
Experiment with levels once you are done with the smart object editing to achieve the desired brightness and contrast.
Plays with Blend Mode, Colors and Saturation to achieve best effect.
You can crop the image to achieve different looks.