He could remove federal policy that force private agencies to go against their beliefs when placing children for adoption. That is not a rollback of gay rights but a restoration of the rights of children and the proper place of the federal government in such decisions.
IMHO that's what he's going to do. He's going to rescind Obama's EO that required every state and every agency to promote Homo marriage and adoption. That's not the same thing as banning it, but the lefties will scream.