Most horses can be retrained to do a new job, and we treat them very much the same as unbroken horses.
Retraining is becoming more common, with plenty of ex-racehorses going on to eventing, showing and polo.
But retraining isn't only for racehorses. Teaching a horse a new discipline means teaching him a whole new set of aids and a new way of doing things, stripping back his knowledge to the basics and building back up from there. It can be difficult for some horses and will take time, but it can also be very rewarding for both horse and rider.