I have 3 off the track horses - they were used by my kids for pony club. Consequently, they did everything.
My old mare was an excellent dressager and could win barrels no problem at all, and a pretty decent campdrafter - she was hopeless at jumping though.
One gelding is an excellent jumper and I was offered a lot of money by someone wanting him for a World Cup mount - but he was my daughters horse and she was enjoying riding him,so he stayed - he was difficult to retrain after 7 years of being a successful racehorse but it was worth the work. He also won prolifically in sporting, could do a blistering barrel time and loved terrorising the cows whilst campdrafting (definately more enthusiasm than finesse).
The other gelding - had he been given the proper chance instead of being a 'spare' - could have excelled in jumping and been a good dressager. He loved sporting. He had one jump school (3 weeks after coming off the track as a 5 yo) and after that he was just dragged out of the paddock when needed and pointed in the direction of whatever was going on and asked to do it. He did, happily and with some success.
To me temperment is everything and the three I have, could (and have) been left in the paddock for months and then just saddled up and ridden without any dramas.
Just train as you would any other horse. I have found thoroughbreds to be excellent at most disciplines because they have been bred to be athletes and a good athlete can usually do athletic things above the average.
Only As Old As You Feel - Sometimes I Feel VERY Old