Vet would be best to advise on this, and an equine vet at that. But I think it is not a good idea.
And if he naturally paces, training him to trot might not be the best thing to do, as I would wonder about any soreness issues.
If you wanted a trotting horse, and one that would jump? You should not have gotten a pacing horse, that has had issues.
Horse was in a rescue twice now? Did you tell them you planned to undo his natural pacing and wanted him to jump?
If they thought he was going to be in a place where you would appreciate him for what he is naturally, I doubt they would be impressed to find out your plans are on something else entirely.
He's already had two strikes against him and ended up in rescue, and what you are trying to do could permanently cripple him.
I just don't understand why you want to do this to a pacing horse.
Horses make me a better person.