this mount should be the normal kelpie from the sales some years ago which means its permanent. As far as I know from my Kelpie (from sales) Im able to choose all skins actually own. I dont think its possible to use skins u dont have.
Anyways if u use any mount as Kelpie, its speed will always be 13 m/sec wich is pretty slow for today standards. All mount abilities like Jumps or Charges are also disabled.