TNG overall never said anything about the Federation or Starfleet being against genetic modification. It wasn’t just Darwin Research Station. They didn’t say anything about it in “Masterpiece Society” either.
Dr. Bashir I Presume was the first episode that any kind of ban was ever brought up. They didn’t even say anything about a ban in “Space Seed” or “Wrath of Khan.”
Also, when Torres was pregnant in Voyager, she wanted the Doctor to modify her baby to remove Klingon traits and no one said it was illegal.