That would be a ridiculous "law" to have. The Federation has no right to tell anyone who can or can't get married.
The Federation has ruled that you can't change your own genome, why should this law be any different? If they don't want any dangerous augmented people running around, they have every right to prevent it from happening. Else why were Sarina, Jack and the other Augments locked away in a institution? For being good?
Which novel was it? I'm either behind (true) or can't remember shit (also true).
Send Sarina awaaaaaaaaaay... let her grow, develop, have other relationships and then bring her back to Julian
It was creepy as on screen but I did love how it showed how Julian Bashir was not immune to some of the obsessive thought spirals his fellow augments suffered from. And I don't think there's any reason they couldn't get together in the decently in the future future.
They could get together in the future, weather or not they both can have kids is another question.