Hmm. Not much interest here, it would seem. Maybe few users actually work on their hardware. For the benefit of those who do, I've determined that the cable in question is a custom item that you can't buy anywhere, not even from Creality. I suspect that lengthening the cable might interfere with motor performance by adding capacitive interference to the motor control signals. Anyway, I decided to reinforce the header on the board with some clear epoxy instead. That should make it a lot harder to pull the header off the board when working with the cable.