Won't work. Waverider tried using temporal energy on him when he was H/P.
Depends on the DD. At his best, they can't do anything but BFR or maybe the soul gem.
Regarding tampering with his DNA, the only time someone has done that is after Imperiex Prime slagged him to a skeleton. Darkseid had his scientists work on him and graft a k-nite weakness in. But then, that's new god tech.