Two Form 1 for making a rifle, such as an SBR. Two pictures, two fingerprint cards, might as well send two certificates of compliance, and get your LEO sign off. Yes, you can switch back and forth on the uppers and if you wish to permanently go back to a non-SBR all it takes is a letter to the ATF informing them of the switch. Yes you can do this on a pre-ban or a post-ban. No, you cannot add the banned goodies once an SBR on a post-ban rifle. It is still a rifle, and as such still bound by the AW ban which does not allow you to add the flash suppressor or bayonet lug, doing so will make it an illegal assault weapon even though it is an NFA firearm. Only by making it a machine gun, which is not a rifle, can you add the fun stuff. If you do this on a pre-ban lower, then you can put on a pre-ban upper with all the goodies, even if it is SBR, but not on a post-ban lower.