It's a CYOA, not a tabletop RPG. After a point, you should just use your imagination and your own interpretation of the text.
I think Flesh Sculptor could make someone infertile by effectively producing the 'physical change' of giving the target the effect of a tubal ligation / vasectomy. Since it's not really a change to the physical properties, it should be fine.
I personally would also be okay with trying to create the infertile effect by making one's testes / ovaries simply produce 'blanks', but one could argue that this would be considered a change to their 'physical properties', so it's probably not allowed.