Unless you tumble after sizing/depriming then it would not be possible to deprime the brass with another case inside. It would have jammed up in the die.
I've deprimed cases with another case stuck inside several times over the last 20 years. The decapping pin just punches through the primer in the inside case. Only way you can tell is that the ram doesn't come quite all the way up by about 1/8", the handle doesn't go quite all the way down. I'm loading on a Dillon 650 progressive so it's very noticeable in that it doesn't allow it to quite stroke far enough to allow the press to trip the cam to advance to the next position.
Loading on a single stage (or a progressive) with the decapping pin sticking out far enough would easily allow you to deprime a case with the next smaller caliber stuck inside it. Shouldn't be any problem loading it up with a small charge of fast powder, the volume wouldn't be reduced enough to notice.