I've never taken one of these down, but in the gun shops they appear to be the same as 10-22 rifle actions, even take the same mag. So I suppose if'n a person had one bought as a "pistol" & he had an old beater 10-22 rifle & sold the barrel, then the action on the Charger got swapped with the old 10-22 rifle action ( repair/fix/mod?--hypothetical) the only real diff would be a serial number & then there'd be potential for a problem. Right?
If he put it in the rifle stock with the short barrel it would be an sbr and need a stamp. If he put a 16" barrel on it and put it in a rifle stock it would be legal, and he could swap it back and forth as he pleased.