Are you asking about using .020 os rings on standard pistons going into standard size bores with some wear in the bore? You could file the rings to get the end gaps about right, but to manufacture a piston ring so it has a .020 larger diameter, the ring is processed on a larger mandrel, that results in a larger ring with a ring tension constant with a standard sized ring. By filing a .020 os ring to fit a standard sized bore, the end gap could be in spec but the ring tension ( pressure on the bore od) will be high,, will it be a disaster, probably not, will it be optimal, certainly not.
