Howdy to the camp.
I have seen photos of Civil War carbines that were re-barreled post-war, into rifles. They still had the staple and ring. Also, someone mentioned that Wilder's men put staples and rings on their rifles.
Just my two cent's worth. If we can shoot carbines in .44 Russian, .45 Schofield, 44-40, and 56-50 centerfire instead of 56-50 rimfire, I think we can forgive a staple on a rifle, especially since this was done to some carbines after the Civil War, and therefore has historical basis.