Are you saying simply replacing the stock with a pistol brace on a registered SBR lower makes it a pistol now?Don't even need to do that. If you pull the stock/brace/”shouldering device" or install a longer barrel, it's no longer an SBR and you may travel at will.
But I'm sure that the #WillNotComply crowd was already traveling freely across with their unregistered SBRs anyway, because otherwise they would be hypocrites.