How to copy a Live Photo from your Mac back to an iOS device

Apple's Live Photos are a lot of fun and provide more context than your typical photo. When your iPhone is full of them, you may want to offload your Live Photos to your Mac. That's easy. But what if you have a favorite Live Photo on your Mac and you want to move it back to your iPhone? Reader Jonas Marel has this problem.
How can I transfer my Live Photo from my iPhone 6s to my Mac and back again to my iPhone as a Live Photo? The transfer from my iPhone to my Mac is easy, but I am not able to t