In reply to Phil Lyon:
I've run down the slopes underneath Carn Mor Dearg in the past. Looks a little steep but it's fine.
Tourist path is ok if you're in running shoes; it's painful in boots if you're hurrying.
I believe Ledge Route is also used as a descent but I imagine route-finding will be tricky if you don't know the route well.
Come to that, TR is itself very reversible if you're not in a queue, I would have thought. Haven't reversed it myself, though.