interesting idea there. With the C&R 1911, you should be able to meet the 12020 C&R SBR exemptions, but I don't know on the AW side. Does a temporary conversion kit to rimfire exempt you from centerfire AW rifle regs since it has a stock? And if were also considered a pistol due to the <16" barrel, it wouldn't be a AW pistol since it has no evil features.
As for reg'ing in multiple calibers, AFAIK, the ATF requires you to put a single caliber/length down on the Form 1 now. Various barrel lengths, such as 8-15", are denied regularly and the Form 1 returned for corrections. Once the Form 1 has been approved, you can temporarly change lengths/calibers as you see fit. If you were to permanently change it so that it would no longer be able to match the Form 1, they recommend that you send a clarification letter so that they can update their records.