The way it is used in the second sentence, though requires commas before and after it.
(Though can be confusing; sometimes it requires a comma to separate it from the rest of the sentence, and sometimes it doesn’t. Even though she’d studied, she wasn’t sure she’d get a good score on the test. She only needed a passing grade, though, so she tried not to worry too much.)
Technology has been developed [by zombies? 🙂 ] to allow people to manipulate their own DNA in realtime, within approved legal limits. For truly dedicated hackers, though, there exist underground markets in illegal mods where anything goes, and it usually does.
You don’t need both approved and legal in the first sentence. I’d recommend deleting the former, because obviously if it’s legal, it has been approved by someone.
(The subgenre of biopunk SF contains many potentially fascinating story ideas, and yet some authors write it just like trite pseudo-cyberpunk, but squishier. *sigh*)