lol no he didn't say you had to start over, you merely misread is all.
All that is required of you to transfer your rank from Shadow Jedi Knight to Sith Knight on this board is what Lup quoted in the first part of his post... your ranks on other boards hold no bearing on this conversation, really.
Transfer of rank from one allegience to another has usually always required a lengthy and believeable RP explaining the motives behind the change (if not required, then just simply expected). In addition the RP has usually been expected to detail the journey of the character as he or she experiences the changes in themselves and then embarks on a journey to learn the new ways that they have just embraced.
So just worry about doing that to the best of your ability, and submit the RP to the Force Council when it is completed. We are not looking for you to arbitrarily change the past of your character - that *would* require starting over. We are looking for an RP in which you explore and develop the changes in your character as she turns from Shadow Jedi to Sith. Not much to ask, really. It's customary for a good RPer to do such things anyways, since this is about RPing...
Then pending a review and decision by the Force Council, the rank will become official (Sith Knight, if you were worried). Really all the Force Council will be looking for is whether you really put some time, thought and development into your character in the RP, or if you were just in a hurry to get it done to fulfill the requirement and didn't do a very good job. So calm down, nothing is being taken from you. Just go out there and RP like usual, show us what you can do since we last saw you, and you'll have no problem I am sure.