I had figured this out somewhat on my own on GameCube.
I have a level 200 Kalki mag alright and I have a FOmar named Alanon, I gave my Kalki mag to my character Rendlan a RAmar for an extreme boost in technique usage (I was overpowering his mst to gain lvls quickly) I was working on making the mag's stats completely full (Star Atomizer is the only thing that does it) I fed it one star atomizer and being it was 200 it shouldn't change, right? It then evolved into this tadpole looking mag off of a HUmar that's a Pinkal (weird that mag last time I checked was a force mag)
Anyway's Mag's as long as they are not set to a Rare, they will evolve regardless the level.
Like my Sato I gave it monomate until 12 def, fed it antidote until 38 dex, difluid until 12 mind, and dimate until 37 pow. Transfered to a FOnewearl made into a Sato and transfered it back to my RAmar and kept feeding it, it stayed as a Sato.
As well feeding Mag's deepends on the I.D. Class not the character class, so in the situation above if the guy wanted a twin mag I would've done a Rati. (Too me after loving that mag for 6-8 years I hate it, I like Sato's that'll probably change soon)
But I hope this helps sorry if its confusing