I did try adjusting the sizing collar down on my MEC 600 and it not did make a difference. I just need to ultimately switch over to the Cheddite hulls and for the time being figure out a way to remove the .002” on the AA’s.
If you start filing the rims on those cases, do you not run the risk of compromising the case and blowing a hole? That's folded steel or brass, and if the former, you will also encourage corrosion.
It's a no brainer to hone the rim recess. It just isn't worth the trouble or risk of rupturing a case. But they are your eyeballs (hopefully safely behind glasses).
I’ve seen shotgun hulls with no metal head, so I doubt the plated steel has any structural function.
If AA cases are a must, I would go the extra mile on resizing.
If not, just use a brand of cases that work.
Modifying the gun would be my last choice, just because there’s always the chance of something going wrong, even a UPS screw-up.
Lovely gun, OP.