The Society is in the enviable position of constantly being able to make up new rules as they wish. What I can say is that in my 50 years in the 'truth' I never came across someone who got baptised a second time, though I do know of very many who were disfellowshipped or DA'ed who came back.
Personally, my baptism vows were the old wording - so my baptism was not a case recognising myself as one of Jehovah's Witnesses, merely acknowledging myself as a sinner who would hence forth seek to do God's will. Seems to me that I could take that vow to almost any other religion!