Such an experiment would be highly unethical and of doubtful interest. After all, you already know sexuality develops without influence, is it useful to know if it develops differently under pressure? To do so it requires to possibly ruin people’s live, that’s why it’s not done.

Also, we already have the opposite experience: gays being convinced to be straight. As far as I know, it doesn’t really work and only creates suppressed emotions that ruins their sexuality.