AR Pistol Build

I have a question. I know that you can not use a lower that has ever been used on a rifle to make a pistol, but can you use a pistol lower to make into a rifle after it has been used on a pistol?

Also can you buy a lower that is marked as a pistol and turn it into a rifle?

 

No not the legal route. No stock on a pistol and no short barrel on a rifle without a Tax Stamp