One method would be to convert that half to a smart object, and duplicate the smart object. Then flip horizontally, and rotate -90 degrees.
Any change you make in either one (by editing the smart object) is reflected in the other half.
Unfortunately, Photoshop’s smart objects cannot be edited in place (they open in a new window), nor do they update in realtime. So for this type of work it is rather inconvenient.
Photoline’s virtual layers are far more efficient: the original source layer can be edited in place, and changes do update all the clones in real-time.
You will have to live with Photoshop’s limitations in this case.
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