I don't know for certain. But I'm pretty sure that you can't.
If sexuality is biological, congenitally-existing, like eye-color or ear shape, then your certainty about change would be reasonable. But as the research is showing over and over (consider the links I offered you), there has been no concrete biological source for homosexuality, no genetic origin for the behavior, that has been found.
These people converted to Christianity, did they not? A religion that doesn't allow people to be openly gay. It's far more likely that these people put the religion before their own desires.
But this
assumes your premise, which is that these people can't change. Contrary to your assumed premise, however, their lives (and a growing number of others, besides) demonstrate that homosexuality is not on par with unchangeable physical features of a human being. If you insulate your assumption from this truth by the rather ad hoc retort that they still want to be homosexual deep-down, then you're forming a kind of unfalsifiable point of view, which always has the effect of blinding you to the truth. If nothing can demonstrate to you that your view is in error, and you are actually in error, you'll never be able to see this, right?
I put
God before my desires, not my religion. Being a Christian is, after all, primarily about interacting with my Maker, not merely abiding by a set of religious propositions and rituals. In my experience of genuine (that is, biblical) fellowship with God, I've encountered a radical change of my desires and thinking on the most fundamental level of who I am. As God works in me His will and way (
Philippians 2:13), the old, selfish, sinful desires, thoughts and behaviors of my past dissolve, replaced by the life of the Holy Spirit who is conforming me more and more to the truth of God's word and the Person of Jesus Christ. It's a big job he has to do in me, but doing it he is!
One of the things that has marked God's work in me, as opposed to my efforts of self-improvement, is that God brings His awesome, universe-creating power to bear in the changes He enacts within me. This has produced a kind of change that has astonished me because it has not involved the teeth-gritting, stuffing down of my sinful desires and impulses, a frightful, constant wrestling with myself, as was the case in the past. If this is the sort of change God has worked in those former homosexuals I mentioned to you, the change goes all the way down, right to the bottom of who they are. And so, they can say, as the apostle Paul did to the former homosexuals in the church at Corinth:
1 Corinthians 6:9-11
9 Or do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived; neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor homosexuals,
10 nor thieves, nor the covetous, nor drunkards, nor revilers, nor swindlers, will inherit the kingdom of God.
11 Such were some of you; but you were washed, but you were sanctified, but you were justified in the name of the Lord Jesus Christ and in the Spirit of our God.
2 Corinthians 5:17
17 Therefore if anyone is in Christ, he is a new creature; the old things passed away; behold, new things have come.
There are plenty of gay people that suppress their own sexuality outside of Christianity as well. For one reason or another. Usually because it's more socially acceptable to be straight.
This is the sort of self-restriction I'd expect from a person who has no access to the heart-transforming, life-changing power of God. It is always what happens when a sinner tries to restrain their sin-nature. When God goes to work on a sinner, though, He deals with
the source of sin in the sinner, not just the effects that the source produces (sin). Homosexuality is just one of the many effects, you see, produced by the source of all of a person's sin. Lying, anger, laziness, pride, sexual sin, resentment, anxiety, etc. - these are all just symptoms of a deeper problem: Self in control. When God goes to work on His children, He goes straight to Self, to the "old man," the person we are outside of God's control, and deals with our sin-problem by doing something about Self on the throne of our hearts. No person disconnected from God can benefit from what He does for all of His children in this regard.