It won't alter the underlying genetic condition, but there has been at least one case report that taking these CFTR modulators during pregnancy can improve the condition of the fetus/newborn:
Both of these babies are female. I am not at all surprised that the drug helped in the way described in the articles, but it doesn't actually indicate whether or not it could impact the vas deferens since that's a defect in the male reproductive tract.
According to the CF Foundation, the cause of the lack of the vas deferens is not conclusively known.
According to the CF Foundation, the cause of the lack of the vas deferens is not conclusively known.
https://www.cff.org/managing-cf/fertility-men-cf