If you're asking if you can power both loops from the same power pack with one pair of wires reversed, so trains on two loops run in the opposite direction to each other the answer is YES. Forget about diodes.
I did the same thing way back when in the olden days when all I had was two HO sets: an Athearn passenger set on the outside loop, a Marx freight set on the inside loop.
However, you won't have independent control of each train. They will both respond to your throttle at the same time; Start, Stop and run at approximately the same speed depending on the locomotives.
It would be better to pick up a second power pack for your new loop, which would allow for independent control of each loop.
Rusty
UPDATE: I missed seeing your video as you've already accomplished your goal. But I still would recommend a second power pack for independent control.
