If someone has spinal injuries, or damage to the spinal cord itself, it will not make any difference when it comes to practising Spinal Breathing Pranayama.
They would have be able to practice in the same way as anyone else.
Even if someone is paralysed from the neck down, they would still be able to practice.
As long as they can breathe and trace the spine with their attention, that will be enough for the practice to work.