On evening while we were teens, my brother and I set to the task of sitting on the handlebars and facing backwards, and relearn to ride the bike. We were able to accomplish this in an evening. If I were to try it today, I could still ride the bicycle like this. It was an interesting experience!
We did not experience any problems riding frontwards again, perhaps sitting on the handlebars ensured that we were not confusing the reverse balancing requirements.
I have not worked too hard at it, but I have not conquered the unicycle.