To date I've converted about 600 or so 9mm cases to 9 x 18 Mak. it's one of the easiest cartridge case conversion there is to do especial with all that free 9mm brass lying around. Before 9mm Mak. brass was available one of the older Speer reloading manuals actualy used the process of trimming down once fired 9mm brass for cases.
I trim my cases with a Lyman lathe trimmer that I added the optional powder adapter to,paid around $15 for it several years ago,it makes short work of trimming lots of cases. To identify my 9mm vs. Mak. cases I simply run the tip of a sharpie around the groove of the primed primer pockets on the Mak. cases.
Some other option are to use nickel plated case for the Mak. brass or use a differ brand of primer with a brass,copper old Wolf SP primer or nickel plated cup material. This allow you to sort your brass before tumbling.
I'm lucky enough to be able to shoot in the back yard so no worries about somebody getting there hands on my converted cases. I use a cable stretched along my shooting lane with a old trampoline net that about 10 ft. high and 15 ft. long to knock down my brass.