Help! Feeding my mag a cell

[Rukh]

I have a level 160 mag whom i want to keep feeding to gain in power and some in DEX. I have a 213 mag cell and I want to have my cool mag, but If I feed it to my mag now, will my mag evolve back to a shitty creature after i feed it some more stuff later? Will it than be ruined? or do I need to wait untill its level 200 to feed it to my mag?

Let me know

-Rukh