Yes. I know that you can have a SBR removed from the registry.
I don't know what, if any, paperwork you have to submit. Never felt the need to have any of my short barrels get longer. I do know it can be done, I have seen a Uzi that was un-SBRed for sale in the past.
"9mm has a very long history of being a pointy little bullet moving quickly" --Sevens