I've been thinking about this since your raised the point and we went over the chapter in the CBS.
Consider: Is there any Scripture that shows this step is required by God? If it is not required by God but it is required by Jehovah's Witnesses (specifically by the Governing Body), then who is it that actually requires dedication?
That is it in a nutshell. I think you've proved to a reasonable degree (at least to me) that the WTS has in fact added to scripture when dealing with the baptism requirements. Why doesn't this cause more issues with current JWs? I think because if you are convinced (as both of us once were) that JWs are Gods chosen people and the GB/FDS is Gods channel on earth today, then you don't have a problem with them adding additional requirements. Why? Because, Jehovah must have directed them to do so. That would be just fine with me if the GB/FDS could actually prove that they have Holy Spirit. Paul, Peter, the other apostles and leaders of the early Christians could prove they had Holy Spirit by performing miracles.
The only "miracle" they can point to is the legal manuvering that got Rutherford and the other WTS directors out of prison in 1919. Now, compare that prison release with Paul's release and conversion of the jailer. Hmm, slightly different senario right? I would expect that Jesus selecting a group of individuals to represent him on earth would be a much grander event or at least on par with the 1st Century events.
Even the outpouring of Holy Spirit at Pentacost 33 CE. Why wasn't there something similar reported after Jesus allegedly inspected his "house" or all organizations claiming to be Christian and chose the Bible Students? Wouldn't the prophsey in Joel have a second application that coordinates with this second coming? Seems to me it would.
I really think that some JWs could conceed the fact that the WTS has added to the scriptures regarding numerous things, including baptism, yet still not be bothered that much by it because of the claim that they are God's chosen ones.
That's why my recent discussions with my wife have been surrounding 607. That date being off and the society misrepresenting secular sources they say support 607 is the lynchpin to JW doctrine. Pull that out and show the deciet, I think the whole thing falls apart. Then, once free, I'm planning on studying all these doctrines to see if ANY of them hold water. My guess is that most do not.
Great subject and I love your questions to consider.