This official news post is copied verbatim from the WoTMUD website. It is copyrighted by wotmud.org.
You can already name horses when you buy one, but once stabled that was impossible, until now.
For a small fee (1-3 gcs) LS can re-name their warhorse, bloodstock or Domani razor in Four Kings at the stables of the Dancing Cartman inn.
For a small fee (1-3 gcs) SS can re-name their warhorse, bloodstock, Domani razor or, if clanned there, their torm or armored stallions in Falme, east of the stables.
Lead your current warhorse etc. to the room and:
SAY NAME X Gloo
Where x is: warhorse, bloodstock, razor, armored, torm.
Be sure to remove any horse eq and have sufficient cash in your inventory, else your current horse will be purged and you will not get the named horse in return.