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.
"No, it's not a silencer. This little doodad is my own invention. I call it a loudener." --Sledge Hammer