That's a valid point. Anyone who uses range brass without looking it over carefully before they load is going to have trouble anyway. In the past I have not marked the bases because I do not have a 9mm. I mark my hot 38 S&W loads with an orange marker, maybe I'll do the same with my 9x18's.Cutting down 9x19 brass is a long and honored tradition among 9x18 shooters.
The other end of the process is not mentioned very often, though - the (at least moral) duty NOT to leave those cut down empty cases, still headstamped "9mm Luger," lying around the range for some 9x19 shooter to pick up and reload for HIS 9x19 guns. If you already "lose" more cases than you would like to admit, think about what'll happen to those cut down cases of yours.
It's my understanding that the MAK is a little larger in diameter than the para; do you have to fire form your cut down brass, or just jam the bullet (also a little fatter) down into it and let it fireform itself?I make my 9x18 brass from 9x19 brass I find at the range....By trimming down free brass the lost pieces do not hurt so much.