My MAG was originally a Lyra, but it turned into a Antlia about 10 minutes ago. I checked the stats when I noticed it, and I'm going to hypothesis that if you get a stat 5 higher than your previously highest stat, then it'll become something different. So originally I mostly just fed it weapons (mostly hunter weapons), since I had a lot of extra weapons, but eventually I had tons of disks that I couldn't use, I started feeding it that. Now, the strike support stat is 12, and the ability support stat is 17.

I am curious, has anyone else discovered this yet?

I think that your mag has the ability to change to any of the four different mags every five levels between levels 30-95 as long as you have one stat higher than whatever the previous dominant stat was.