EntropiaBones:Is it possible to be demoted in rank ?
No. It seems that these days you are allowed to restart though, (I'm most confident this is true on apple devices) you'd lose whatever you've bought/got in the way of equipment and apparel. In fact if you were doing this it'd be as well to sell everything you can, gift balls to a friend and maybe get them gifted back to the new player.
I don't think the above (restarting) should be allowed but I do think it is, I'm just not entirely sure on which platforms.